Re: Symbolica package warning: Using rat() heuristics for double-precision input (is this what you wanted?)

[Colin Macdonald]

On 17/02/17 08:18, Doug Stewart wrote:
>     I am thinking of putting this on the wiki.

Good idea!  I can help edit.

But first, the essential pattern here is:

1.  Do a symbolic calculation (in this case, a derivative)
2.  Evaluate that result for double values.

"subs" is not really the right tool for this.  It makes symbolic 
substitutions.

Perhaps the right pattern here is:

>> df = diff(...)
>> dfh = function_handle(df)
>> dfh(3.1415927)

Here "dfh" is a regular plain-old Octave anonymous function, can be 
evaluated efficiently for doubles, etc.

Note: you can also write this as "dfh = matlabFunction(df)" for 
compatibility with the Matlab Symbolic Toolbox.

There is some discussion about all this in 
https://github.com/cbm755/octsympy/issues/121

cheers,
Colin