MemoryError: Unable to allocate 40.9 GiB for an array with shape (74121, 74121) and data type float64

[kaibozhu]

x=(N,) or (N,1) is different, (N,) is a vector, and (N,1) is an array, when we use matrix-vector multiply for an array with shape (74121,74121), this should be matrix-free. it doesn't work due to MemoryError, but it can work for gmres from scipy. I think this LinearOperation maybe some different with LinearOperation of scipy ?