(Matlab Coder)Domain error. To compute complex results from real x, use 'acosd(complex(x))'

Question

cui,xingxing 2023-9-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026804-matlab-coder-domain-error-to-compute-complex-results-from-real-x-use-acosd-complex-x

评论： cui,xingxing 2023-9-28

When I try to evaluate an acosd value, the generated mex execution is not consistent with the original function and often errors out?

function out = triFun(in)%#codegen
out = real(acosd(in));
end

I use the following statement to generate successfully：

codegen -config:mex triFun.m -args {0.5}

Then test it with the following statement:

for i = 1:10
    a = rand(1,2);
    b = a;
    distA = sqrt(a(1).^2+a(2).^2);
    distB = sqrt(b(1).^2+b(2).^2);
    val = dot(a,b)./(distA.*distB);
    out1 = triFun(val) % always OK
    out2 = triFun_mex(val) % sometimes failed, Domain error. To compute complex results from real x, use 'acosd(complex(x))' ???
end

output error:

test_codegen_mex

out1 =

0

Domain error. To compute complex results from real x, use 'acosd(complex(x))'.

Error in acosd (line 13)

coder.internal.error('Coder:toolbox:ElFunDomainError',mfilename);

Error in triFun (line 2)

out = real(acosd(in));

Error in test_codegen_mex (line 12)

out2 = triFun_mex(val) % sometimes failed, Domain error. To compute complex results from real x, use 'acosd(complex(x))' ???

Question:

Obviously, the a,b I gave are equal and the val value should be equal to 1. There will be no complexity, but out2 will mistake the result for a complex number and out1 will not. How can I modify this to achieve the goal of consistent results?

Run In Matlab R2023a

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Answer 1

Bruno Luong 2023-9-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2026804-matlab-coder-domain-error-to-compute-complex-results-from-real-x-use-acosd-complex-x#answer_1321039

编辑：Bruno Luong 2023-9-28

在 MATLAB Online 中打开

"Obviously, the a,b I gave are equal and the val value should be equal to 1"

wrong. Before claming anything, you should first check.

format long
while true
    a = rand(1,2);
    b = a;
    distA = sqrt(a(1).^2+a(2).^2);
    distB = sqrt(b(1).^2+b(2).^2);
    val = dot(a,b)./(distA.*distB);
    if abs(val) > 1
        a
        b
        val
        exceedvalto1 = val-1
        fprintf('val can not be == 1 with numerical error\n')
        break
    end
end
a = 1×2
   0.894442198246962   0.268453115545912
b = 1×2
   0.894442198246962   0.268453115545912
val = 
   1.000000000000000
exceedvalto1 = 
     2.220446049250313e-16
val can not be == 1 with numerical error