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Function Argument Validation, Compare to Irrational Number or Expression

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Toder
Toder on 28 Apr 2020
Commented: Adam Danz on 29 Apr 2020
Is there a way to use MATLAB's built-in validation functions to compare an argument to an expression or funciton output?
I want to do the following:
function out = myfun(x)
arguments
x (1,1) double {mustBeGreaterThan(x,pi)}
end
out = foo;
end
Since pi is a function, which is not allowed in the native validation functions, the above code throws an error. Instead I have to define a custom validation function to compare the argument to pi.
function out = myfun(x)
arguments
x (1,1) double {mustBeGreaterThanPi(x)}
end
out = foo;
end
function mustBeGreaterThanPi(x)
if x <= pi
error('Value must be greater than pi.')
end
end
The validation block cannot pass pi to the custom validation function, so pi must be built into the function. This is a complete pain in the neck if we want to compare, say, ten arguments to ten different irrationals, repeating decimals, or simple expressions; we must define ten custom validation functions, unless we get creative with passing scalars or strings (we could pass c to the validation function where an error is thrown if value <= c*pi, for example).

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Accepted Answer

Adam Danz
Adam Danz on 28 Apr 2020
Edited: Adam Danz on 29 Apr 2020
One solution would be to replace the pi function with a literal;
arguments
x (1,1) double {mustBeGreaterThan(x,3.1415926535897932384626)}
end
or you could use a different form of validation,
function out = jff(x)
assert(x>pi, 'x must be greater than pi')
out = x*2;
end
function out = jff(x)
validateattributes(x,{'double'},{'scalar','>',pi})
out = x*2;
end

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Adam Danz
Adam Danz on 29 Apr 2020
Agreed. The arguments method of input validation is still new (released in r2019b) so perhaps it will be expanded upon in future releases. Most of my functions are designed to run in as many releases of Matlab as possible so I haven't used the arguments method of validation. I suggest you make a service request for this feature.

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