The power funciton in math function block does not correctly work.

Question

kj g 2020-9-12

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https://ww2.mathworks.cn/matlabcentral/answers/592525-the-power-funciton-in-math-function-block-does-not-correctly-work

回答： Ameer Hamza 2020-9-12

I choosed the signed power. If the power is even, the output always keeps positive. It works well if the power is not even. I wonder what happens when the power is even. Is it a bug?

The input u this example is a sine wave signal and v is 2, 3, 6, respectively. Please look the scope in the figure, when the power is even, it keeps positive. It is strange. I don't know if this exmaple works correctly on other machines.

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Answer 1

Ameer Hamza 2020-9-12

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https://ww2.mathworks.cn/matlabcentral/answers/592525-the-power-funciton-in-math-function-block-does-not-correctly-work#answer_493468

There seems to be a bug in the implementation of Signed Power functionality in the case of integer powers. You may consider filing a bug report: https://www.mathworks.com/support/bugreports/report_bug. Meanwhile, you can create your own block using power and sign blocks

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Answer 2

BOB MATHEW SYJI 2020-9-12

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https://ww2.mathworks.cn/matlabcentral/answers/592525-the-power-funciton-in-math-function-block-does-not-correctly-work#answer_493453

When “signed power” is checked, it first calculates the power of absolute value of input and then multiplies it with sign of the input. You can find more on: https://www.mathworks.com/help/simulink/slref/mathfunction.html

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kj g 2020-9-12

编辑：kj g 2020-9-12

Surely I know this, sign(u)*|u|^v. The input u this example is a sine wave signal and v is 2, 3, 6, respectively. Please look the scope in the figure, when the power is even, it keeps positive. It is strange. I don't know if this exmaple works correctly on other machines.

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