I figure I'll put this here, rather than embedding it in the midst of other
threads.

I'm currently working out some code to create some piece-wise functions with
very specific constraints.

During development, I noticed some odd mismatches, seemingly resulting from the
manner in which 3-argument select () statements work.

Using the 4-argument form and (repeating the equation to evaluate after a comma)
doesn't seem to correct this.

Specifically, each section of the piece-wise function never reaches the end of
its domain, and instead, the next section of the nested select statement starts
getting evaluated.
I shifted the 2nd segment up a bit to illustrate the problem in the attached
image. (disregard the file name)

https://wiki.povray.org/content/Reference:Numeric_Expressions
select(A, B, C [,D])
It can be used with three or four parameters Select compares the first argument
with zero, depending on the outcome it will return B, C or D. A,B,C,D can be
floats or fun(c)tions.
When used with three parameters, if A < 0 it will return B, else C (A >= 0).
When used with four parameters, if A < 0 it will return B. If A = 0 it will
return C. Else it will return D (A > 0).



Maybe that's something that I'm doing wrong, or maybe there's a hidden issue
with select () that's never been uncovered yet.

But it did make me think that there ought to be a way to reverse which "side" of
the evaluation A = 0 gets included in:

When used with three parameters (in the reverse case), if A <= 0 it will return
B, else C (A > 0).


Also, in past projects I have run into situations where I'd like to use matrix
transforms but with variable arguments.

Exposure of the elements of a matrix to SDL would be helpful when trying to
apply multiple matrix transforms to something and intermediate stages need to be
debugged, or simple matrix calculations need to be performed, letting
POV-Ray/yuqk do the heavy lifting.

Freya Holmer just put out another video on multiplying vectors, and mentioned
how when working with octonions, simply swizzling vector components allowed
rapid calculations to be performed using that "trick".

Vector swizzling (Vec.zxy) would be handy

Vector functions would be positively worth paying for.
Both user-defined, and inbuilt.
vectors allowed as arguments, vector components as arguments, and vector
results.
sin (<x, y, z>) ought to give me a result of <sin x, sin y, sin z>

Allowing arrays to be referenced or processed by functions would be great as
well.

Vector sizes and elements in things like prisms ought to be versatile and/or
standardized.  Having to convert points to a 2D vector is a PITA.

Access to data types would be great.
agnostic input data type for #read would be excellent as well.
There's also the issue of determining the number of elements in a vector.

Lots of functions in math.inc that ought to be inbuilt.

Lots more I'm sure.  Don't worry, I'll think of them   ;)

- BW

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