Python ValueError: operands could not be broadcast together with shapes

Question

I am doing SVD and when I try to run my code I get the following error:

ValueError: operands could not be broadcast together with shapes (375, 375) (375, 500)

I am using an image with size (500, 375)

Here is my code:

from PIL import Image
from Image import new
from numpy import *
import numpy as np
from scipy.linalg import svd

im = Image.open("lake.tif")
pix = im.load()
im.show()
r, g, b = im.split()
R = np.array(r.getdata())
R.shape = (500, 375)
Ur, Sr, VrT = svd(R.T, full_matrices=False)
R1 = Ur * diag(Sr) * VrT

Solution

You are doing component wise product. Either make those things matrices or use:

 R1 = np.dot(Ur, np.dot(diag(SR), VrT))

or use something like:

Ur, Sr, VrT = map(np.asmatrix, (Ur, diag(Sr), Vrt))
R1 = Ur * Sr * VrT

Which is much cleaner if you do a lot of matrix products (like in this line), otherwise arrays are typically preferable since they are the base type. If you prefer you can of course also just call np.asmatrix on each itself.

Comments

[Pierre GM]

you should probably describe how to transform a ndarray into a matrix and explain that for matrix objects, multiplication works as expected...