Question

Is there a way to use numpy.linalg.det or numpy.linalg.inv on an nx3x3 array (a line in a multiband image), for example? Right now I am doing something like:

det = numpy.array([numpy.linalg.det(i) for i in X])

but surely there is a more efficient way. Of course, I could use map:

det = numpy.array(map(numpy.linalg.det, X))

Any other more direct way?

Answer 1

I’m pretty sure there is no substantially more efficient way than what you have. You can save some memory by first creating an empty array for the results and writing all results directly to that array:

res = numpy.empty_like(X) 
for i, A in enumerate(X):
    res[i] = numpy.linalg.inv(A)

This won’t be any faster, though — it will only use less memory.