triinv.c

speech signal process tools

triinv(T,Tinv,n)	/* T and Tinv upper triangular */
		/* 0 normal return, 1 T singular */
register int n;
register double *T,*Tinv;
{
	register int i,j,k,iT,kT;
	register double sum,dtemp,*sT,*sTinv;

	j=n+1;
	for(i=0,sT=T,sTinv=Tinv;i<n;i++,sT+=j,sTinv+=j)
		{
		if(!*sT)return(1);
		*sTinv=1/(*sT);
		}
	for(j=n-1;j>=0;j--)
		{
		for(i=j-1,iT=(j-1)*n;i>=0;i--,iT-=n)
			{
			sum=0;
			for(k=i+1,kT=(i+1)*n;k<j+1;k++,kT+=n)
				sum+=T[iT+k]*Tinv[kT+j];
			dtemp= -sum*Tinv[iT+i];
			Tinv[iT+j]=dtemp;
			}
		}
	for(i=0;i<n;i++,Tinv+=n)/* clear lower triangle */
		{
		for(j=0,sT=Tinv;j<i;j++,sT++)
			*sT=0;
		}
	return(0);
}