Cheng Chien-Wen

I cannot figure out how jit.op functions. I use jit.op to multiply two matrix but the resulted matrix does not seem to be mathematically right. For example, the 6th cell of the left matrix is 255, the 6th cell of the right matrix is 100, and the resulted value from jit.op with multiplication function is 99 instead of 25500.

question-about-jit-op

It is because you are working with a matrix of type char.

Char type is a value between 0 and 255, correponding in a multiplication to 0 and 1.

When you multiply by a char, between 0 and 255, it means that 0 multiply by 0, 255 by 1 and for exemple multiply by 128 correspond to multiply by 0.5.

25500 does not exist in char type. If you want the results you describe, try to change your matrix in type long, or float32.

It is because you are working with a matrix of type char.
Char type is a value between 0 and 255, correponding in a multiplication to 0 and 1.

25500 does not exist in char type. If you want the results you describe, try to change your matrix in type long, or float32.


Quote: David Buff wrote on Tue, 08 April 2008 05:15

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> It is because you are working with a matrix of type char.

> Char type is a value between 0 and 255, correponding in a multiplication to 0 and 1.

> When you multiply by a char, between 0 and 255, it means that 0 multiply by 0, 255 by 1 and for exemple multiply by 128 correspond to multiply by 0.5.

> 25500 does not exist in char type. If you want the results you describe, try to change your matrix in type long, or float32.

Thank you so much. Now I understand it better.

Quote: David Buff wrote on Tue, 08 April 2008 05:15
----------------------------------------------------
> It is because you are working with a matrix of type char.
> Char type is a value between 0 and 255, correponding in a multiplication to 0 and 1.
>
> When you multiply by a char, between 0 and 255, it means that 0 multiply by 0, 255 by 1 and for exemple multiply by 128 correspond to multiply by 0.5.
>
> 25500 does not exist in char type. If you want the results you describe, try to change your matrix in type long, or float32.
----------------------------------------------------

Thank you so much. Now I understand it better.


question about jit.op