what's the meaning of debug info: Inputs strides

[Wenpeng Yin]

hello, guys,

Usually, theano will print out some error info if something goes wrong, like:

ValueError: total size of new array must be unchanged

Apply node that caused the error: Reshape{2}(AdvancedSubtensor1.0, TensorConstant{[ 100 4000]})

Inputs shapes: [(0, 200), (2,)]

Inputs strides: [(1600, 8), (8,)]

Inputs types: [TensorType(float64, matrix), TensorType(int64, vector)]

But I can not understand the meaning of "Input strides", could any body give hints?   Thanks a lot! 

[Michael Eickenberg]

Strides encode the number of steps needed in memory to step along a given axis in an array. Numpy works the same way and allows direct access to this information:

In [1]: import numpy as np

In [2]: a = np.arange(30.).reshape(2, 3, 5)

In [3]: a.strides

Out[3]: (120, 40, 8)

In [4]: a.shape

Out[4]: (2, 3, 5)

A step in the last axis consists of 8 bytes (the size of a float64). A step in the second axis consists of 5 * 8 bytes = 40 bytes. A step in the first axis consists of 3 * 5 * 8 bytes = 120 bytes.

This arrangement presupposes C-ordering. In general, the strides contain additional information on how the data is represented in memory which you cannot deduce solely from the shape.

Hope this helps a little,

Michael

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[Wenpeng Yin]

thank you Michael, it helps much.

Best.

************************************************************************************

Wenpeng Yin

Homepage:http://sites.google.com/site/yinwenpeng1987/

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