[Numpy-discussion] numpy.clip behavior at max and min of dtypes

Edward C. Jones edcjones at comcast.net
Tue Jun 5 19:37:51 EDT 2012

Can the following function be written using numpy.clip?  In some other way?
Does numpy.clip satisfy condition 4 below?  Does numpy.clip satisfy some
closely related condition?

Define a function clipcast:
     output = clipcast(arr, dtype=None, out=None)

1. All arrays have int or float dtypes.

2. Exactly one of the keyword arguments "dtype" and "out" must be used.  If
"dtype" is given, then output has that dtype.

3. "output" has the same shape as "arr".

4. Let ER be the set of all the real numbers that can be exactly represented
by the output dtype.  ER is finite and bounded.  Let themin = min(ER) and
themax = max(ER).  For any real number x, define a function f(x) by

    If x is in ER, define f(x) = x.

    If x is between two consecutive numbers, u and v, in ER, then define
       f(x) = u or f(x) = v.  Probably the choice would be made using a C

    If x < themin, define f(x) = themin.

    If x > themax, define f(x) = themax.

If x is an element of arr, say Arr[I], then output[I] == f(x) where I is any
index that defines a single element of arr.

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