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compile - Catching error in middle of evaluation of compiled function



I have programmed and Compileed a complicated numerical function. The function has singularities (i.e. are infinite) at certain input numerical values. I need to catch this problem in the middle of the evaluation and return a more meaningful Message to the user than the default CompiledFunction::cfne.


I can't quite understand the answer to This Question. Would someone help me the following concrete example?


f = Compile[{{x, _Real}, {y, _Real}}, 
 Log[(x - y^2 - 2. x)^2]/(y x^2 - 2 (x + y) - y^2 + 3.)]

For certain values, there are singularities:


f[-196, 14]


CompiledFunction::cfn:

Numerical error encountered at instruction 7; proceeding with uncompiled evaluation



and also


f[1.5, 0]


CompiledFunction::cfne:
Numerical error encountered; proceeding with uncompiled evaluation.

Power::infy: Infinite expression 1/0. encountered.



I would like to trump these default error messages with my own. Is it possible to do this without compromising the speed of the evaluation??



I feel that using a giant If statement such as:


funcForUser::msg = "Singular point.";
funcForUser[x_, y_] := If[x != y^2, f[x, y], Message[funcForUser::msg]; Undefined]

is a very ugly way to solve the problem. And I also don't have the patience to track down all possible conditions that lead to singularities.



Answer



How about using "RuntimeErrorHandler":


f = Compile[{{x, _Real}, {y, _Real}}, 
   Log[(x - y^2 - 2. x)^2]/(y x^2 - 2 (x + y) - y^2 + 3.), 
   "RuntimeOptions" -> {"RuntimeErrorHandler" -> Function[Throw[$Failed]]}

];

Catch[Quiet@f[-196, 15]] // AbsoluteTiming
(* {0.000019, 0.0000116843} *)

Catch[Quiet@f[-196, 14]] // AbsoluteTiming
(* {0.000051, $Failed} *)

Edit


We can even have specific messages too:



(* Copying Ted Ersek's messages *)
f::log="The expression f[`1`,`2`] lead to Log[0.0] which evaluates to -\[Infinity].";
f::div="The expression f[`1`,`2`] lead to division by zero which evaluates to ComplexInfinity.";

f = Compile[{{x, _Real}, {y, _Real}}, 
   Log[(x - y^2 - 2. x)^2]/(y x^2 - 2 (x + y) - y^2 + 3.), 
   "RuntimeOptions" -> {"RuntimeErrorHandler" -> Function[{x,y},
      Which[x-y^2-2. x==0,
        Message[f::log,x,y];
        -\[Infinity],

       y x^2-2 (x+y)-y^2+3.==0,
        Message[f::div,x,y];
        ComplexInfinity,
       True,
        Indeterminate
      ]
    ]}
];

f[-196, 14]

CompiledFunction::cfn: Numerical error encountered at instruction 7; proceeding with uncompiled evaluation. >>
f::log: The expression f[-196,14] lead to Log[0.0] which evaluates to -\[Infinity].
(* -\[Infinity] *)

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