Get the data in rows and/or columns from a matrix in a MEX file
4 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Hello,
I am writing a MEX routine in which I need to multiply a row and a vector from a matrix (among other things). In Matlab's language it would look like this:
tmp(i) = A(i,:) * A(:,i)
I want to use the ddot BLAS function. Is there a MEX function to get a complete row/column from a matrix?
0 Kommentare
Akzeptierte Antwort
James Tursa
am 16 Dez. 2013
The signature for ddot from this link:
is:
DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
* .. Scalar Arguments ..
INTEGER INCX,INCY,N
* ..
* .. Array Arguments ..
DOUBLE PRECISION DX(*),DY(*)
* ..
So you can just give the starting address (DX and DY) and increment (INCX and INCY) of each, no need to extract anything. E.g., a code snippet for calling to do the basic calculation could be this:
// Assume 1st input prhs[0] is A, 2nd input prhs[1] is i
mwSignedIndex N, I, ONE;
double *pr, *DX, *DY;
double tmp;
ONE = 1;
N = mxGetN(prhs[0]); // assume input matrix is square
pr = mxGetPr(prhs[0]); // assume input matrix is double
I = mxGetScalar(prhs[1]);
DX = pr + (I-1); // Use 0-based indexing
DY = pr + (I-1)*N;
tmp = ddot(&N,DX,&N,DY,&ONE); // A(i,:)*A(:,i)
Weitere Antworten (0)
Siehe auch
Kategorien
Mehr zu Write C Functions Callable from MATLAB (MEX Files) finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!