# where is the mistake?

1 view (last 30 days)
Amer Al-Maashani on 18 Jan 2021
Edited: Amer Al-Maashani on 18 Jan 2021
ezplot('int((x*x*normpdf(x,1,2)))',[-20 20 0 2])

Walter Roberson on 18 Jan 2021
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])
Amer Al-Maashani on 18 Jan 2021
Edited: Amer Al-Maashani on 18 Jan 2021
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