where is the mistake?

Question

Amer Al-Maashani 2021-1-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/719535-where-is-the-mistake

编辑： Amer Al-Maashani 2021-1-18

采纳的回答： Walter Roberson

ezplot('int((x*x*normpdf(x,1,2)))',[-20 20 0 2])

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Answer 1

Walter Roberson 2021-1-18

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https://ww2.mathworks.cn/matlabcentral/answers/719535-where-is-the-mistake#answer_600010

在 MATLAB Online 中打开

What is being integrated? What is the lower bound? What is the upper bound?

Your use of [-20 20 0 2] suggests that you are expecting to plot over two dimensions. As you have an integral, that would require three variables, with one of them being the variable of integration. Your expression only has one variable, and it would be used as the variable of integration if the integral worked, leaving you with two extra variables.

Remember that int() is strictly for symbolic integration.

syms x

f = int((x*x*normpdf(x,1,2)))

f =

ezplot(f,[-20 20 0 2])

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Amer Al-Maashani 2021-1-18

编辑：Amer Al-Maashani 2021-1-18

Have a look to the plot for that

>> syms x

>> f = int((x*x*normpdf(x,1,2)))

f =

(5629499534213120*2^(1/2)*pi^(1/2)*erf(2^(1/2)*(x/4 - 1/4)))/5644425081792261 - (4503599627370496*x*exp(- x^2/8 + x/4 - 1/8))/5644425081792261 - (4503599627370496*exp(- x^2/8 + x/4 - 1/8))/5644425081792261

>> ezplot(f,[-20 20])

I got it as it should be.

Thanks a lot

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