How do I use multiple inputs in mexcuda?

I found a mexGPUExample.cu and compiled it successfully. In this file, there is only one input and one output. But I'd like to verify multiple inputs and single outputs. Changed codes are as below:

/*
 * Example of how to use the mxGPUArray API in a MEX file.  This example shows
 * how to write a MEX function that takes a gpuArray input and returns a
 * gpuArray output, e.g. B=mexFunction(A).
 *
 * Copyright 2012 The MathWorks, Inc.
 */

#include "mex.h"
#include "gpu/mxGPUArray.h"
#include "matrix.h"
/*
 * Device code
 */
void __global__ TimesTwo(double const * const A, double const* const C, double * const B, int const N)
{
    /* Calculate the global linear index, assuming a 1-d grid. */
    int const i = blockDim.x * blockIdx.x + threadIdx.x;
    if (i < N) {
        B[i] = 2.0 * A[i];
        B[i+N] = 2.0 * C[i];
       
    }
    
}

/*
 * Host code
 */
void mexFunction(int nlhs, mxArray *plhs[],
                 int nrhs, mxArray const *prhs[])
{
    /* Declare all variables.*/
    mxGPUArray const *A, *C;
    mxGPUArray *B;
    double const *d_A, *d_C;
    double *d_B;
    int N;
    char const * const errId = "parallel:gpu:mexGPUExample:InvalidInput";
    char const * const errMsg = "Invalid input to MEX file.";

    /* Choose a reasonably sized number of threads for the block. */
    int const threadsPerBlock = 256;
    int blocksPerGrid;

    /* Initialize the MathWorks GPU API. */
    mxInitGPU();

    /* Throw an error if the input is not a GPU array. */
    if ((nrhs!=1) || !(mxIsGPUArray(prhs[0]))) {
        mexErrMsgIdAndTxt(errId, errMsg);
    }

    A = mxGPUCreateFromMxArray(prhs[0]);
    C = mxGPUCreateFromMxArray(prhs[1]);
    /*
     * Verify that A really is a double array before extracting the pointer.
     */
    if (mxGPUGetClassID(A) != mxDOUBLE_CLASS) {
        mexErrMsgIdAndTxt(errId, errMsg);
    }

    /*
     * Now that we have verified the data type, extract a pointer to the input
     * data on the device.
     */
    d_A = (double const *)(mxGPUGetDataReadOnly(A));
    d_C = (double const *)(mxGPUGetDataReadOnly(C));
    /* Create a GPUArray to hold the result and get its underlying pointer. */
    mwSize ndim = 2, dims[2] = {2,4};
    B = mxGPUCreateGPUArray(ndim,
                            dims,
                            mxGPUGetClassID(A),
                            mxGPUGetComplexity(A),
                            MX_GPU_DO_NOT_INITIALIZE);
    d_B = (double *)(mxGPUGetData(B));

    /*
     * Call the kernel using the CUDA runtime API. We are using a 1-d grid here,
     * and it would be possible for the number of elements to be too large for
     * the grid. For this example we are not guarding against this possibility.
     */
    N = (int)(mxGPUGetNumberOfElements(A));
    blocksPerGrid = (N + threadsPerBlock - 1) / threadsPerBlock;
    TimesTwo<<<blocksPerGrid, threadsPerBlock>>>(d_A, d_C, d_B, N);

    /* Wrap the result up as a MATLAB gpuArray for return. */
    plhs[0] = mxGPUCreateMxArrayOnGPU(B);
    
    /*
     * The mxGPUArray pointers are host-side structures that refer to device
     * data. These must be destroyed before leaving the MEX function.
     */
    mxGPUDestroyGPUArray(A);
    mxGPUDestroyGPUArray(B);
    mxGPUDestroyGPUArray(C);
}

There is all changed codes.

And then I'll type in matlab mexcuda xxx.cu, the matlab tell me compiled successfully. Then I provide two matrix and tansfer them to GPU. Finally, the question is typing xxx(data_gpu1,data_gpu2) will report an error: Invalid input to MEX file. I would like to know how to make xxx.cu recognize multiple inputs.

Answer 1

[Joss Knight]

You have passed in two inputs but you have a check if (nrhs!=1), so you are erroring because you don't have one input. You need to change that bit.

[jsbbs hsyhs]

Thank you for your generous answer!