Error "assignment to expression with array type" when using C script to handle complex number with mex.

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JasonLuo 2018-1-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/379181-error-assignment-to-expression-with-array-type-when-using-c-script-to-handle-complex-number-with

评论： JasonLuo 2018-1-27

Initialize pointer

/*Input variables*/
      double *kloc_r;
      double *kloc_i;
      double *img_r;
      double *img_i;

Assign the complex numbers to array my_plan.f_hat[] whose element's type is double complex.

      for(int i = 0; i < row; i++){
          for(int j = 0; j < col; j++){
              double real = img_r[(j*row + i)];
              double imag = img_i[(j*row + i)];
              my_plan.f_hat[(j*row + i)] = real +_Complex_I*imag;
          }
      }

Assign double numbers to array my_plan.x[] whose element's type is double.

    for(j = 0; j < my_plan.M_total; j++){
        my_plan.x[2*j + 0] = kloc_r[j];
        my_plan.x[2*j + 1] = kloc_i[j];
    }

When compiling, it alerts me with following error.

error: assignment to expression with array type: my_plan.f_hat[(j*row + i)] = real +_Complex_I*imag;

Source Code

#include "mex.h"
#include "nfft3.h"
#include <stdio.h>
#include <stdlib.h>
#include <complex.h>
void mexFunction(int nlhs, mxArray *plhs[],
    int nrhs, const mxArray *prhs[]){
      if(nrhs!=2){
          mexErrMsgTxt("Usage: res = nfft(kloc, img)");
          return;
      }
      /*Input variables*/
      double *kloc_r;
      double *kloc_i;
      double *img_r;
      double *img_i;
      /*Output variables*/
      double *kval_r;
      double *kval_i;
      /*Initialization*/
      kloc_r = mxGetPr(prhs[0]);
      kloc_i = mxGetPi(prhs[0]);
      img_r = mxGetPr(prhs[1]);
      img_i = mxGetPi(prhs[1]);
      plhs[0] = mxCreateDoubleMatrix(mxGetM(prhs[0]), 
                                     mxGetN(prhs[0]), mxCOMPLEX);
      kval_r = mxGetPr(plhs[0]);
      kval_i = mxGetPi(plhs[0]);
      int i, j;
      int row = mxGetM(prhs[1]);
      int col = mxGetN(prhs[1]);
      int M = mxGetM(prhs[0]) * mxGetN(prhs[0]);
      /* two dimensional nfft */
      nfft_plan my_plan;
      nfft_init_2d(&my_plan, row, col, M);
      /*Get image(time domain)*/
      for(int i = 0; i < row; i++){
          for(int j = 0; j < col; j++){
              my_plan.f_hat[(j*row + i)] = img_r[(j*row + i)] +
                                           _Complex_I*img_i[(j*row + i)];
          }
      }
      /*Get k-space trajectory*/
      for(j = 0; j < my_plan.M_total; j++){
          my_plan.x[2*j + 0] = kloc_r[j];
          my_plan.x[2*j + 1] = kloc_i[j];
      }
      if(my_plan.flags & PRE_PSI)
          nfft_precompute_psi(&my_plan);
      /*Apply transform*/
      nfft_trafo(&my_plan);
      /*Output k value*/
      for(j = 0; j < my_plan.M_total; j++){
          kval_r[j] = creal(my_plan.f[j]);
          kval_i[j] = cimag(my_plan.f[j]);
      }
      nfft_finalize(&my_plan);
  }
Error

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James Tursa 2018-1-26

Please post the code for the definition of the variables involved. Also, please do NOT post screen shots of code. We can't run screen shots. Please replace your screen shots with actual text that you highlight and use the "{ } Code" button to format.

JasonLuo 2018-1-27