函数是cyclic.c
.
void cyclic(float a[], float b[], float c[], float alpha, float beta,
float r[], float x[], unsigned long n)
// Solves for a vector x[1..n] the “cyclic” set of linear equations. a,
//b, c, and r are input vectors, all dimensioned as [1..n], while alpha and beta are //the corner
// entries in the matrix.
我对 Matlab 和 C 之间的接口很陌生。而且我已经好几年没有使用 C 了。
昨晚,我完成并编译。最后一件事是调用它。
#include "mex.h"
#include "nrutil.h"
#define FREE_ARG char*
#define NR_END 1
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#define NR_END 1
#define FREE_ARG char*
void nrerror(char error_text[])
/* Numerical Recipes standard error handler */
{fprintf(stderr,"Numerical Recipes run-time error...\n");
fprintf(stderr,"%s\n",error_text);
fprintf(stderr,"...now exiting to system...\n");
exit(1);
}
float *vector(long nl, long nh)
/* allocate a float vector with subscript range v[nl..nh] */
{
float *v;
v=(float *)malloc((size_t) ((nh-nl+1+NR_END)*sizeof(float)));
if (!v) nrerror("allocation failure in vector()");
return v-nl+NR_END;
}
void free_vector(float *v, long nl, long nh)
/* free a float vector allocated with vector() */
{
free((FREE_ARG) (v+nl-NR_END));
}
void tridag(float a[], float b[], float c[], float r[], float u[],
unsigned long n)
{
unsigned long j;
float bet,*gam;
gam=vector(1,n);
if (b[1] == 0.0) nrerror("Error 1 in tridag");
u[1]=r[1]/(bet=b[1]);
for (j=2;j<=n;j++) {
gam[j]=c[j-1]/bet;
bet=b[j]-a[j]*gam[j];
if (bet == 0.0) nrerror("Error 2 in tridag");
u[j]=(r[j]-a[j]*u[j-1])/bet;
}
for (j=(n-1);j>=1;j--)
u[j] -= gam[j+1]*u[j+1];
free_vector(gam,1,n);
}
void cyclic(float a[], float b[], float c[], float alpha, float beta,
float r[], float x[], unsigned long n)
{
void tridag(float a[], float b[], float c[], float r[], float u[],
unsigned long n);
unsigned long i;
float fact,gamma,*bb,*u,*z;
if (n <= 2) nrerror("n too small in cyclic");
bb=vector(1,n);
u=vector(1,n);
z=vector(1,n);
gamma = -b[1]; //Avoid subtraction error in forming bb[1].
bb[1]=b[1]-gamma; //Set up the diagonal of the modified tridiagonal
bb[n]=b[n]-alpha*beta/gamma; //system.
for (i=2;i<n;i++) bb[i]=b[i];
tridag(a,bb,c,r,x,n);// Solve A · x = r.
u[1]=gamma;// Set up the vector u.
u[n]=alpha;
for (i=2;i<n;i++) u[i]=0.0;
tridag(a,bb,c,u,z,n);// Solve A · z = u.
fact=(x[1]+beta*x[n]/gamma)/ //Form v · x/(1 + v · z).
(1.0+z[1]+beta*z[n]/gamma);
for (i=1;i<=n;i++) x[i] -= fact*z[i]; //Nowget the solution vector x.
free_vector(z,1,n);
free_vector(u,1,n);
free_vector(bb,1,n);
}
void mexFunction(int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[])
{
float *a,*b,*c,*x,*r;
float alpha,beta;
unsigned long n = (unsigned long) mxGetScalar(prhs[6]);
// a=mxGetPr(prhs[0]);
// b=mxGetPr(prhs[1]);
// c=mxGetPr(prhs[2]);
// r=mxGetPr(prhs[5]);
a = (float*) mxGetData(prhs[0]);
b = (float*) mxGetData(prhs[1]);
c = (float*) mxGetData(prhs[2]);
r = (float*) mxGetData(prhs[5]);
// alpha=*(mxGetPr(prhs[3]));
// beta=*(mxGetPr(prhs[4]));
alpha = (float) mxGetScalar(prhs[3]);
beta = (float) mxGetScalar(prhs[4]);
plhs[0]= mxCreateDoubleMatrix(n, 1, mxREAL);
x = mxGetPr(plhs[0]);
mexPrintf("%f ",alpha);
mexPrintf("\n");
mexPrintf("%f ",beta);
mexPrintf("\n");
mexPrintf("%d ",n);
mexPrintf("\n");
cyclic(a,b,c, alpha, beta,r,x,n) ;
mexPrintf("%d ",n);
mexPrintf("\n");
}
最后我成功编译了cyclic(a,b,c, alpha, beta,r,x,n) ;
。但答案是不对的。我认为这是因为r
是一个虚向量。所以我的问题是我应该如何在之间转换 rC
and Matlab
?