Undefined function 'piecewise' for input arguments of type 'double'. or 'Conversion to logical from sym is not possible.' errors

Question

Phuquy Bui 2020-2-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/505370-undefined-function-piecewise-for-input-arguments-of-type-double-or-conversion-to-logical-from

回答： Ajay Pattassery 2020-2-18

function deflectionV=Deflection_ptbui3(deflPos)
syms deflPos 
deflectionV=piecewise((0<deflPos)&&(deflPos<=120),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4,(120<deflPos)&&(deflPos<=240),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4+(2.5*(deflPos-120)^4),(240<deflPos)&&(deflPos<=360),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4+(2.5*(deflPos-120)^4)+(600*(deflPos-240)^3));
deflectionV=(1/3.19E9)*deflectionV;
end

This is my code for the function for my piecewise, but whenever I call for it in my actual script, I get a 'Conversion to logical from sym is not possible.' error.

I've been trying to do this problem where i put the user input into a piecewise function.

Before when I didn't have the syms, it would also just give me 'Undefined function 'piecewise' for input arguments of type 'double'. So i'm not entirely sure whats going on and my teacher nor TA's know very much about the function. And if you think it isn't gonna work, please let me know so I can get the closure to delete this mess of a function. :)

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Answer 1

Ajay Pattassery 2020-2-18

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/505370-undefined-function-piecewise-for-input-arguments-of-type-double-or-conversion-to-logical-from#answer_416078

在 MATLAB Online 中打开

The logical operator && is a short-circuit operator which means the second operand is only evaluated when the result is not fully determined by the first operand. Refer here for more information.

In your case logical and (&) need to be used.

deflectionV=piecewise((0<deflPos)&(deflPos<=120),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4,(120<deflPos)&(deflPos<=240),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4+(2.5*(deflPos-120)^4),(240<deflPos)&(deflPos<=360),800*(deflPos)^3-13.68*10^6*(deflPos)-2.5*(deflPos)^4+(2.5*(deflPos-120)^4)+(600*(deflPos-240)^3));