How can I solve this problem in the matlab program ?

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

What problem? You show some text from some theory work; you do not show any question to be solved.

[Vuqar Samedov]

Dear Walter Roberson, I use it in the matlab program, but the answer is not correct. I do not know why the answer is incorrect? The answer should actually be 1.

>> syms x a b

>> f=1/b*sqrt(2*pi)*exp(-1/2*b^2)*(x-a)^2;

>> u=(1/b*sqrt(2));

>> f=subs(f,u);

>> int (f,-inf,inf)

ans =

NaN

[Timo Dietz]

Some parenthesis are missing and u seems to be wrongly defined. Nevertheless, Matlab seems to calculate intemediate steps which prevents the final elimination of values on symbolic side.

Answer 1

[David Hill]

It does equal 1

syms u
int(exp(-u^2),-inf,inf);

[Timo Dietz]

Yes it does, but he substitution does not work as expected. Even with all parenthesis set and u defined correctly, Matlab seems to calculate intermediate values (e.g. sqrt(2)) and finally is not able to eliminate these.

Answer 2

[Walter Roberson]

syms x a b u
Pi = sym(pi)

Pi = 

π

f = 1/(b*sqrt(2*Pi))*exp(-1/(2*b^2)*(x-a)^2)

f = 

U = (x-a)/(b*sqrt(2));
DU = diff(U,x);
B = solve(u == U, b)

B = 

fs = subs(f/DU, b, B)

fs = 

int(fs,-inf,inf)

ans = 

1