[Gretl-devel] Re: special syntax for "end of matrix"

On Tue, 14 Sep 2021, Riccardo (Jack) Lucchetti wrote: > On Tue, 14 Sep 2021, atecon wrote: > >> One question: How would such an "end" operator work "under the hood"? >> a) Is it triggering the computation of rows(X) AND cols(X) each time >> "end" is called, or >> b) is it a property of matrix X, meaning that once X is initialized, >> the number of rows and columns is automatically computed and this >> information stored as a property of the object X? > > It's (b). The computational cost of the rows() and cols() function is > nearly zero. The "matrix" struct definition is in > lib/src/gretl_matrix.h, line 77. Exactly zero, I'd say. In hansl you need to call rows() or cols() to get the dimensions of a matrix but internally, in C, rows and cols are members of the matrix struct so no computation is required, just a read.