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meg_leadfield1.c
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Wed, May 28, 06:07

meg_leadfield1.c
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#include <string.h>
#include <math.h>
#include "mex.h"
void
mexFunction (int nlhs, mxArray * plhs[], int nrhs, const mxArray * prhs[])
{
mxArray *lf;
double tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7, eps, alpha, beta, A, B, C;
double r[3], u[3], d[3];
double *lf_p, *rm_p, *um_p, *R;
int nchan, i;
char str[256];
if (nrhs<3)
mexErrMsgTxt("Not enough input arguments");
if (nrhs>3)
mexErrMsgTxt("Too many input arguments");
if (mxGetM(prhs[0])!=1 || mxGetN(prhs[0])!=3)
mexErrMsgTxt ("Invalid dimension for input argument 1");
if (mxGetN(prhs[1])!=3)
mexErrMsgTxt ("Invalid dimension for input argument 2");
if (mxGetN(prhs[2])!=3)
mexErrMsgTxt ("Invalid dimension for input argument 3");
nchan = mxGetM(prhs[1]);
if (mxGetM(prhs[2])!=nchan)
mexErrMsgTxt ("Number of channels does not match between argument 2 and 3");
lf = mxCreateDoubleMatrix(nchan, 3, mxREAL);
lf_p = mxGetData(lf);
R = mxGetData(prhs[0]);
rm_p = mxGetData(prhs[1]);
um_p = mxGetData(prhs[2]);
eps = mxGetEps();
tmp2 = sqrt(R[0]*R[0] + R[1]*R[1] + R[2]*R[2]); /* norm(R) */
for (i=0; i<nchan; i++)
{
/* get the position of this single channel */
r[0] = rm_p[i];
r[1] = rm_p[i+nchan];
r[2] = rm_p[i+nchan+nchan];
/* get the orientation of this single channel */
u[0] = um_p[i];
u[1] = um_p[i+nchan];
u[2] = um_p[i+nchan+nchan];
/* compute the difference between this channel and the dipole position */
d[0] = r[0] - R[0];
d[1] = r[1] - R[1];
d[2] = r[2] - R[2];
tmp1 = sqrt(r[0]*r[0] + r[1]*r[1] + r[2]*r[2]); /* norm(r) */
/* tmp2 = sqrt(R[0]*R[0] + R[1]*R[1] + R[2]*R[2]); */
tmp3 = sqrt(d[0]*d[0] + d[1]*d[1] + d[2]*d[2]); /* norm(d) */
tmp4 = r[0]*R[0] + r[1]*R[1] + r[2]*R[2]; /* dot(r, R) */
tmp5 = r[0]*d[0] + r[1]*d[1] + r[2]*d[2]; /* dot(r, d) */
tmp6 = R[0]*d[0] + R[1]*d[1] + R[2]*d[2]; /* dot(R, d) */
tmp7 = tmp1*tmp2*tmp1*tmp2 - tmp4*tmp4; /* norm(cross(r,R))^2 */
alpha = 1 / (-tmp3 * (tmp1*tmp3+tmp5));
A = 1/tmp3 - 2*alpha*tmp2*tmp2 - 1/tmp1;
B = 2*alpha*tmp4;
C = -tmp6/(tmp3*tmp3*tmp3);
if (tmp7<eps)
beta = 0;
else
beta = ((A*r[0] + B*R[0] + C*d[0])*u[0] +
(A*r[1] + B*R[1] + C*d[1])*u[1] +
(A*r[2] + B*R[2] + C*d[2])*u[2]) / tmp7;
/* re-use the temporary array d for something else */
d[0] = alpha*u[0] + beta*r[0];
d[1] = alpha*u[1] + beta*r[1];
d[2] = alpha*u[2] + beta*r[2];
/* lf(i,:) = 1e-7 * cross(alpha*u + beta*r, R) */
lf_p[i ] = (d[1]*R[2] - d[2]*R[1])*1e-7;
lf_p[i+nchan ] = (d[2]*R[0] - d[0]*R[2])*1e-7;
lf_p[i+nchan+nchan] = (d[0]*R[1] - d[1]*R[0])*1e-7;
}
/* assign the output parameter */
plhs[0] = lf;
return;
}

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