passing a matrix from R to C code
Erin, you seem to confuse R and C syntax a bit, among other things. See below.
On Mon, Sep 24, 2012 at 3:03 PM, Erin Hodgess <erinm.hodgess at gmail.com> wrote:
Dear R People:
I'm working on a project that will pass a matrix from an R function to
a C subroutine.
I tried to write the following:
#include<R.h>
#include<Rinternals.h>
void lu1(int *n, float *a, float *b, float *ab)
{
int i,k,j,p,na=*n+10;
float sum, l[200][200],u[200][200]z[200];
Comma missing?
for(i=0;i<na;i++) {
for(j=0;j<na;j++) {
l[i,j]=0.0;
u[i,j]=0.0;
In C you must write l[i][j] and u[i][j]. l[i,j] is actually equal to l[j] and that's an array of 200 doubles.
}
z[i] =0.0;
}
//********** LU decompositio*n *****//
for(k=1;k<=*n;k++)
{
u[k][k]=1;
for(i=k;i<=*n;i++)
{
sum=0;
for(p=1;p<=k-1;p++)
sum+=l[i][p]*u[p][k];
l[i][k]=a[i][k]-sum;
a is a single-index array. You cannot index it using two indices. Convert the two into one using something like i*dimension + k. Same below. HTH, Peter
}
for(j=k+1;j<=*n;j++)
{
sum=0;
for(p=1;p<=k-1;p++)
sum+=l[k][p]*u[p][j];
u[k][j]=(a[k][j]-sum)/l[k][k];
}
}
//***** FI*NDI*NG Z; LZ=b*********//
for(i=1;i<=*n;i++)
{ //forward subtitutio*n method
sum=0;
for(p=1<i;p++)
sum+=l[i][p]*z[p];
z[i]=(b[i]-sum)/l[i][i];
}
//********** FI*NDI*NG X; UX=Z***********//
for(i=*n;i>0;i--)
{
sum=0;
for(p=*n;p>i;p--)
sum+=u[i][p]*ab[p];
ab[i]=(z[i]-sum)/u[i][i];
}
}
And here is the output:
R CMD SHLIB lu1.c
gcc -std=gnu99 -I/usr/share/R/include -DNDEBUG -fpic -O3 -pipe
-g -c lu1.c -o lu1.o
lu1.c: In function ?lu1?:
lu1.c:15:8: error: incompatible types when assigning to type
?float[200]? from type ?double?
lu1.c:16:8: error: incompatible types when assigning to type
?float[200]? from type ?double?
lu1.c:33:25: error: subscripted value is neither array nor pointer nor vector
lu1.c:41:26: error: subscripted value is neither array nor pointer nor vector
make: *** [lu1.o] Error 1
erin at ubuntu:~$
I'm thinking that the matrix is hanging things up.
Does this look familiar, please?