# 2-D histogram: Density matrix values in their correct position.

Hi Viktor, you indicated in the lesson on Histograms in NumPy (part 2) that in the density array returned by the np.histogram2d() function there is a slight rotation because the rows of said array correspond to the X bins and the columns to the Y bins. In other words, the rows are swapped with the columns with respect to a visual representation.

Using Python and Numpy features I wrote a line of code that repositions the values of the density matrix so that it corresponds directly, without rotations, with its graphical representation in the X, Y coordinate plane.

The code is as follows,

np.array(list(map(lambda row: row[::-1], dm))).T

dm, is de density array.

dm = np.histogram2d(matrix_A[0], matrix_A[1], bins=4)[0]

And I ask you about it if you agree with me that the resulting matrix in this case is the density array that fully corresponds to its graphical representation in the X, Y plane and that this matrix is practically also giving us the visual representation of the corresponding 2-D histogram

1 answers ( 0 marked as helpful)

I added some graphs and, at least for the lesson example, I see that the graph clearly looks like the repositioned value density matrix: