Method invert

deps/opencv/modules/core/src/lapack.cpp:932–1182

#define Dd( y, x ) ((double*)(dstdata + y*dststep))[x]

double cv::invert( InputArray _src, OutputArray _dst, int method )
{
    bool result = false;
    Mat src = _src.getMat();
    int type = src.type();

    CV_Assert(type == CV_32F || type == CV_64F);

    size_t esz = CV_ELEM_SIZE(type);
    int m = src.rows, n = src.cols;

    if( method == DECOMP_SVD )
    {
        int nm = std::min(m, n);

        AutoBuffer<uchar> _buf((m*nm + nm + nm*n)*esz + sizeof(double));
        uchar* buf = alignPtr((uchar*)_buf, (int)esz);
        Mat u(m, nm, type, buf);
        Mat w(nm, 1, type, u.data + m*nm*esz);
        Mat vt(nm, n, type, w.data + nm*esz);

        SVD::compute(src, w, u, vt);
        SVD::backSubst(w, u, vt, Mat(), _dst);
        return type == CV_32F ?
            (((float*)w.data)[0] >= FLT_EPSILON ?
             ((float*)w.data)[n-1]/((float*)w.data)[0] : 0) :
            (((double*)w.data)[0] >= DBL_EPSILON ?
             ((double*)w.data)[n-1]/((double*)w.data)[0] : 0);
    }

    CV_Assert( m == n );

    if( method == DECOMP_EIG )
    {
        AutoBuffer<uchar> _buf((n*n*2 + n)*esz + sizeof(double));
        uchar* buf = alignPtr((uchar*)_buf, (int)esz);
        Mat u(n, n, type, buf);
        Mat w(n, 1, type, u.data + n*n*esz);
        Mat vt(n, n, type, w.data + n*esz);

        eigen(src, w, vt);
        transpose(vt, u);
        SVD::backSubst(w, u, vt, Mat(), _dst);
        return type == CV_32F ?
        (((float*)w.data)[0] >= FLT_EPSILON ?
         ((float*)w.data)[n-1]/((float*)w.data)[0] : 0) :
        (((double*)w.data)[0] >= DBL_EPSILON ?
         ((double*)w.data)[n-1]/((double*)w.data)[0] : 0);
    }

    CV_Assert( method == DECOMP_LU || method == DECOMP_CHOLESKY );

    _dst.create( n, n, type );
    Mat dst = _dst.getMat();

    if( n <= 3 )
    {
        uchar* srcdata = src.data;