# Category Cublas matrix inversion

## Cublas matrix inversion

In linear algebraan n -by- n square matrix A is called invertible also nonsingular or nondegenerate if there exists an n -by- n square matrix B such that. A square matrix that is not invertible is called singular or degenerate. A square matrix is singular if and only if its determinant is zero.

### CUTLASS: Fast Linear Algebra in CUDA C++

Singular matrices are rare in the sense that the probability that a square matrix whose real or complex entries are randomly selected from any finite region in the number line or complex plane is singular is 0, that is, it will "almost never" be singular. However, in some cases such a matrix may have a left inverse or right inverse. Matrix inversion is the process of finding the matrix B that satisfies the prior equation for a given invertible matrix A.

While the most common case is that of matrices over the real or complex numbers, all these definitions can be given for matrices over any ring. However, in the case of the ring being commutative, the condition for a square matrix to be invertible is that its determinant is invertible in the ring, which in general is a stricter requirement than being nonzero. For a noncommutative ring, the usual determinant is not defined. The conditions for existence of left-inverse or right-inverse are more complicated since a notion of rank does not exist over rings.

Let A be a square n by n matrix over a field K for example the field R of real numbers. The following statements are equivalent, that is, for any given matrix they are either all true or all false:.

The rows of the inverse matrix V of a matrix U are orthonormal to the columns of U and vice versa interchanging rows for columns. This property can also be useful in constructing the inverse of a square matrix in some instances where a set of orthogonal vectors but not necessarily orthonormal vectors to the columns of U are known and then applying the iterative Gram—Schmidt process to this initial set to determine the rows of the inverse V.

This is true because singular matrices are the roots of the determinant function. This is a continuous function because it is a polynomial in the entries of the matrix. Thus in the language of measure theoryalmost all n -by- n matrices are invertible. Furthermore, the n -by- n invertible matrices are a dense open set in the topological space of all n -by- n matrices. Equivalently, the set of singular matrices is closed and nowhere dense in the space of n -by- n matrices. In practice however, one may encounter non-invertible matrices. And in numerical calculationsmatrices which are invertible, but close to a non-invertible matrix, can still be problematic; such matrices are said to be ill-conditioned.

Gauss—Jordan elimination is an algorithm that can be used to determine whether a given matrix is invertible and to find the inverse. An alternative is the LU decompositionwhich generates upper and lower triangular matrices, which are easier to invert.

A generalization of Newton's method as used for a multiplicative inverse algorithm may be convenient, if it is convenient to find a suitable starting seed:. Victor Pan and John Reif have done work that includes ways of generating a starting seed. Newton's method is particularly useful when dealing with families of related matrices that behave enough like the sequence manufactured for the homotopy above: sometimes a good starting point for refining an approximation for the new inverse can be the already obtained inverse of a previous matrix that nearly matches the current matrix, for example, the pair of sequences of inverse matrices used in obtaining matrix square roots by Denman—Beavers iteration ; this may need more than one pass of the iteration at each new matrix, if they are not close enough together for just one to be enough.

Newton's method is also useful for "touch up" corrections to the Gauss—Jordan algorithm which has been contaminated by small errors due to imperfect computer arithmetic. If matrix A can be eigendecomposed, and if none of its eigenvalues are zero, then A is invertible and its inverse is given by. If matrix A is positive definitethen its inverse can be obtained as. Writing the transpose of the matrix of cofactorsknown as an adjugate matrixcan also be an efficient way to calculate the inverse of small matrices, but this recursive method is inefficient for large matrices.

To determine the inverse, we calculate a matrix of cofactors:. Inversion of these matrices can be done as follows: .Please read our Introduction to Matrices first. Reciprocal of a Number. The Inverse of a Matrix is the same idea but we write it A Because we don't divide by a matrix! When we multiply a matrix by its inverse we get the Identity Matrix which is like "1" for matrices :. We just mentioned the "Identity Matrix".

It is the matrix equivalent of the number "1":. A 3x3 Identity Matrix. The inverse of A is A -1 only when:. In other words: swap the positions of a and d, put negatives in front of b and c, and divide everything by the determinant ad-bc.

So, let us check to see what happens when we multiply the matrix by its inverse:. Because with matrices we don't divide! Seriously, there is no concept of dividing by a matrix. In that example we were very careful to get the multiplications correct, because with matrices the order of multiplication matters.

AB is almost never equal to BA. Calculations like that but using much larger matrices help Engineers design buildings, are used in video games and computer animations to make things look 3-dimensional, and many other places.

It is also a way to solve Systems of Linear Equations. With matrices the order of multiplication usually changes the answer. Also note how the rows and columns are swapped over "Transposed" compared to the previous example.

It is like the inverse we got before, but Transposed rows and columns swapped over. First of all, to have an inverse the matrix must be "square" same number of rows and columns. We cannot go any further! This Matrix has no Inverse. Such a matrix is called "Singular", which only happens when the determinant is zero.

And it makes sense There needs to be something to set them apart. Hide Ads About Ads. Inverse of a Matrix Please read our Introduction to Matrices first. What is the Inverse of a Matrix?

This is the reciprocal of a number : Reciprocal of a Number. When we multiply a number by its reciprocal we get 1. Imagine we can't divide by numbersWe have decomposed the structure of the GEMM computation into deeper, structured primitives for loading data, computing predicate masks, streaming data at each level of the GEMM hierarchy, and updating the output matrix. Matrix multiplication is a key computation within many scientific applications, particularly those in deep learning. Many operations in modern deep neural networks are either defined as matrix multiplications or can be cast as such.

Matrix multiplication is also the core routine when computing convolutions based on Fast Fourier Transforms FFT  or the Winograd approach . When constructing cuDNN, we began with our high-performance implementations of general matrix multiplication GEMM in the cuBLAS library, supplementing and tailoring them to efficiently compute convolution.

Today, our ability to adapt these GEMM strategies and algorithms is critical to delivering the best performance for many different problems and applications within deep learning. The flexible and efficient application of dense linear algebra is crucial within deep learning and the broader GPU computing ecosystem. Unlike other templated GPU libraries for dense linear algebra e. Our CUTLASS primitives include extensive support for mixed-precision computations, providing specialized data-movement and multiply-accumulate abstractions for handling 8-bit integer, half-precision floating point FP16single-precision floating point FP32and double-precision floating point FP64 types.

Ideally, performance should be limited by the arithmetic throughput of the processor. This leads to the following loop nest. This is a great improvement! Further restructuring offers additional opportunities to exploit both locality and parallelism.

## Invertible matrix

We refer to this concept generally as accumulating matrix products. Here, you can see data movement from global memory to shared memory matrix to thread block tilefrom shared memory to the register file thread block tile to warp tileand from the register file to the CUDA cores for computation warp tile to thread tile. Figure 2 shows the computation performed by a single thread block and highlights the blocks of data used in one iteration of its main loop.

Figure 3 shows a detailed view of the structure of one block-level matrix product. We refer to storage for this output tile as accumulators because it stores the result of accumulated matrix products.

Each accumulator is updated once per math operation, so it needs to reside in the fastest memory in the SM: the register file. Figure 4 shows a detailed view. Figure 4 also depicts data sharing from shared memory among several warps. Consequently, the warp structure is mapped onto operations performed by individual threads.

This leads to a 2D tiled structure within a thread as the detailed view in Figure 5 shows. The 32 cells correspond to the 32 threads within a warp. To maximize compute intensity, this basic structure can be replicated to form the full warp-level accumulator tile, yielding an 8-by-8 overall thread tile computed from an outer product of 8-by-1 and 1-by-8 fragments. This is illustrated by the four accumulator tiles shown in green.

In effect, the WMMA API is an alternative to the thread tile structure described in the previous section for warp-wide matrix multiply-accumulate operations.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. I implemented a parallel algorithm for matrix inversion based on Gauss-Jordan elimination.

In this homework, the algorithm should be implemented with CUDA programs with competitive performance, which should also be compared with equivalent CPU implementations with the serial algorithm. The computed result should be verified by a matrix multiplication to get an identify matrix. Hand in: A CUDA project containing all the necessary source files, as well as a document describing how your parallel algorithm is designed and implemented, with a graph illustrating performance gain over CPU equivalence with respect to the increasing size of the matrices.

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Inverse of a 2x2 matrix - Matrices - Precalculus - Khan Academy

Latest commit. Latest commit f Nov 17, You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Nov 16, Nov 17, GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. I have a rudimentary implementation of a batched matrix inversion op with scikits. As more then 1 person seem to use this, it would be good to move this in Theano. We don't have time for this in the short term. Could someone clear up how one can attempt to replicate the skcuda fft op for something like a linear solver?

Could you check and give just a bit help of making that work? The questions I have are listed there and they include more details of how to actually manage some of the stuff in the operator. Should we build it from source etc Especially useful would be the linear solver, which often is a much better option than an actual inverse, and the symmetric matrix eigen decomposition, alongside SVD.

Are those planned to be included? If you need to use linear solver, you can use GpuCusolverSolve. That would be really appreciated and then it would be easy to directly benchmark theano cusolver and magma ops. I guess also porting the eigenvalue decomposition in addition to the SVD makes sense for the same reasons as above. I don't plan to work on magma linear solver.

I plan to add magma qr and cholesky. If you'll start working on psd inverse, let me know. Take a note, that numpy does not have specialized psd inverse. Ideally, we should have both cpu and gpu versions. Note that however, if I do this it will be on linear solvers, rather than matrix inverses, since they are faster and more numerically stable.

Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. New issue.This library adds flexibility in matrix data layouts, input types, compute types, and also in choosing the algorithmic implementations and heuristics through parameter programmability.

After a set of options for the intended GEMM operation are identified by the user, these options can be used repeatedly for different inputs. For maximum compatibility with existing Fortran environments, the cuBLAS library uses column-major storage, and 1-based indexing. Instead, macros or inline functions should be defined to implement matrices on top of one-dimensional arrays.

## Inverse of a Matrix

For Fortran code ported to C in mechanical fashion, one may chose to retain 1-based indexing to avoid the need to transform loops. Here, ld refers to the leading dimension of the matrix, which in the case of column-major storage is the number of rows of the allocated matrix even if only a submatrix of it is being used.

Starting with version 4. This section discusses why a new API is provided, the advantages of using it, and the differences with the existing legacy API. In general, new applications should not use the legacy cuBLAS API, and existing applications should convert to using the new API if it requires sophisticated and optimal stream parallelism, or if it calls cuBLAS routines concurrently from multiple threads.

For sample code references please see the two examples below. The application must initialize the handle to the cuBLAS library context by calling the cublasCreate function.

Then, the is explicitly passed to every subsequent library function call. Once the application finishes using the library, it must call the function cublasDestroy to release the resources associated with the cuBLAS library context.

This approach allows the user to explicitly control the library setup when using multiple host threads and multiple GPUs. For example, the application can use cudaSetDevice to associate different devices with different host threads and in each of those host threads it can initialize a unique handle to the cuBLAS library context, which will use the particular device associated with that host thread.

Then, the cuBLAS library function calls made with different handle will automatically dispatch the computation to different devices. The device associated with a particular cuBLAS context is assumed to remain unchanged between the corresponding cublasCreate and cublasDestroy calls. In order for the cuBLAS library to use a different device in the same host thread, the application must set the new device to be used by calling cudaSetDevice and then create another cuBLAS context, which will be associated with the new device, by calling cublasCreate.

The library is thread safe and its functions can be called from multiple host threads, even with the same handle. When multiple threads share the same handle, extreme care needs to be taken when the handle configuration is changed because that change will affect potentially subsequent CUBLAS calls in all threads.

It is even more true for the destruction of the handle. However, bit-wise reproducibility is not guaranteed across toolkit version because the implementation might differ due to some implementation changes. This guarantee only holds when a single CUDA stream is active. If multiple concurrent streams are active, the library may optimize total performance by picking different internal implementations. In that case, the results are not guaranteed to be bit-wise reproducible because atomics are used for the computation.

Therefore if they were allocated on the heap, they can be freed just after the return of the call even though the kernel launch is asynchronous. In this case, similarly to matrix and vector results, the scalar result is ready only when execution of the routine on the GPU has completed.

This requires proper synchronization in order to read the result from the host. For example, this situation can arise when iterative methods for solution of linear systems and eigenvalue problems are implemented using the cuBLAS library. The application can conceptually associate each stream with each task. Then, the computation performed in separate streams would be overlapped automatically when possible on the GPU.The intent of cuSolver is to provide useful LAPACK-like features, such as common matrix factorization and triangular solve routines for dense matrices, a sparse least-squares solver and an eigenvalue solver.

In addition cuSolver provides a new refactorization library useful for solving sequences of matrices with a shared sparsity pattern. Not all matrices have a good sparsity pattern for parallelism in factorization, so the cuSolverSP library also provides a CPU path to handle those sequential-like matrices.

For those matrices with abundant parallelism, the GPU path will deliver higher performance. The final part is cuSolverRF, a sparse re-factorization package that can provide very good performance when solving a sequence of matrices where only the coefficients are changed but the sparsity pattern remains the same.

The GPU path of the cuSolver library assumes data is already in the device memory. By now, cuSolverMg supports 1-D column block cyclic layout and provides symmetric eigenvalue solver.

The cuSolverDN library was designed to solve dense linear systems of the form. The cuSolverSP library was mainly designed to a solve sparse linear system. The core algorithm is based on sparse QR factorization. The matrix A is accepted in CSR format. On top of the linear and least-squares solvers, the cuSolverSP library provides a simple eigenvalue solver based on shift-inverse power method, and a function to count the number of eigenvalues contained in a box in the complex plane.

The cuSolverRF library was designed to accelerate solution of sets of linear systems by fast re-factorization when given new coefficients in the same sparsity pattern.

The cuSolverRF library is applicable when the sparsity pattern of the coefficient matrices A i as well as the reordering to minimize fill-in and the pivoting used during the LU factorization remain the same across these linear systems.

The later can be performed using the cuSolverRF library. Notice that because the sparsity pattern of the coefficient matrices, the reordering and pivoting remain the same, the sparsity pattern of the resulting triangular factors L i and U i also remains the same. Therefore, the real difference between the full LU factorization and LU re-factorization is that the required memory is known ahead of time.

The naming convention is as follows:. For example, qr sparse QR factorization is used in linear solver and least-square solver. The cuSolverRF library routines are available for data type double. Most of the routines follow the naming convention:. The cuSolver library functions prefer to keep asynchronous execution as much as possible. Developers can always use the cudaDeviceSynchronize function to ensure that the execution of a particular cuSolver library routine has completed.

A developer can also use the cudaMemcpy routine to copy data from the device to the host and vice versa, using the cudaMemcpyDeviceToHost and cudaMemcpyHostToDevice parameters, respectively. In this case there is no need to add a call to cudaDeviceSynchronize because the call to cudaMemcpy with the above parameters is blocking and completes only when the results are ready on the host.

The libraryPropertyType data type is an enumeration of library property types. CUDA version X. The following code can show the version of cusolver library. The cusolver library uses high precision for iterative refinement when necessary.

This chapter describes how to use the cuSolver library API. It is not a reference for the cuSolver API data types and functions; that is provided in subsequent chapters. The library is thread-safe, and its functions can be called from multiple host threads.

If the application performs several small independent computations, or if it makes data transfers in parallel with the computation, then CUDA streams can be used to overlap these tasks. The computations performed in separate streams would then be overlapped automatically on the GPU, when possible.

This approach is especially useful when the computation performed by a single task is relatively small, and is not enough to fill the GPU with work, or when there is a data transfer that can be performed in parallel with the computation. There is no cudaMalloc inside cuSolver library, the user must allocate the device workspace explicitly.

The floatdoublecuComplexand cuDoubleComplex data types are supported. The first two are standard C data types, while the last two are exported from cuComplex. In addition, cuSolverDN uses some familiar types from cuBlas. This is a pointer type to an opaque cuSolverDN context, which the user must initialize by calling cusolverDnCreate prior to calling any other library function.

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