[Math] Is there a name for this?

[Math] Is there a name for this?

torhu

Member #2,727

September 2002

I'm doing something with NumPy. Is there a name for this?

array = max(array) - array

I want to call it complement, but I don't know if that's right... :'(

APPEND: I'll explain what the code does. It's vector operations, every element in array is subtracted from the max value.

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Mark Oates

Member #1,146

March 2001

I'm assuming this is only useful when your max is a positive number?

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torhu

Member #2,727

September 2002

I guess so, numbers are in the range [0, 1000] in practice.

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Ariesnl

Member #2,902

November 2002

Array is an array and max(array) is a number...
so you are substracting an array from a number ?

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bamccaig

Member #7,536

July 2006

Sounds like a shortcut for Array(max(array), len(array)) - array.

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torhu

Member #2,727

September 2002

It's numpy, so it's a vector operation.

If the array was sorted, it would be the same as reversing the array. But if you have an array [2, 0, 1], the result would be [0, 2, 1].

In pure Python:

a = [2, 0, 1]
maxval = max(a)
a = [maxval - x for x in a]

If the lowest value is not zero you need to compensate:

a = [-2, -1, 1]
maxval = max(a)
minval = min(a)
a = [maxval - x + minval for x in a]

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SiegeLord

Member #7,827

October 2006

I tried looking, but couldn't find anything. I like the name 'complement', perhaps 'max complement' in this case.

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torhu

Member #2,727

September 2002

I ended up just called it complement, doesn't matter much anyway. But thanks. I'll give you a cookie

I was using it when messing around with color schemes for an assignment at uni. We were drawing the Mandelbrot set, and there was a competition for the coolest image 8-)

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