[Octave-bug-tracker] [bug #31974] Interpreter fails to create complex numbers with Inf complex parts

[David Bateman]

Follow-up Comment #8, bug #31974 (project octave):

I had a look at coding this as it seemed to me that everything could be
treated in the function

oct-parse.yy (static tree_expression * fold (tree_binary_expression *))

but the problem is harder than I thought.. We need to treat not just "Inf *
j" but also "Inf * 1j" as the parser treats the first as two identifiers and
the second as an identifier times a constant. However identifier can be
overloaded by user functions and variables, so

Inf = pi;
Inf * j

should return "0 + pi * j" so a simple test of the identifier in the parser
can work. A solution for the above I looked at however is stymied by the case

for i = 1 : 10
  d(i) = Inf * j;
  Inf = pi;'t
endfor

as d(1) should be "0 + Inf * j" but d(2:10) should be "0 + pi * j".

Also another test case for matlab is

x = Inf;
x * j

Does this return "0 + j"  or "NaN + j"? And what about

j = Complex (0, 1);
Inf * j

does it return "0 + j" or "NaN + j"? And finally what about if you create a
user function

function y = fcn ()
  y = Inf;
end

and then run

fcn * j

does it return "0 + j" or "NaN + j"? If the above three cases all return "0 +
j" then the problem should be treated in ov.cc (do_binary_op) rather then in
the parser and the problems above would go away.

D.


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