0 个投票

In my script, I call a function value to input values and put the input in another function integrnfn:
[A,x1,x2]=value;
y=integrfn(A,x1,x2);
fprintf('The value of the integral is %.3f', integrfn(A,x1,x2))
function [A,x1,x2]=value
A=input('Please enter a positive value: ');
x1=input('Please enter another positive value: ');
x2=input('Please enter a positive value that is greater than the previous one: ');
end
function y=integrfn(A,x1,x2)
y=int(A*exp(-x^2)*cos(2*x)/(1+x^2),x,x1,x2);
end
However, when I run it, it says:
Undefined function or variable 'x'.
Error in script >integrfn (line 15)
y=int(A*exp(-x^2)*cos(2*x)/(1+x^2),x,x1,x2);
Error in the script (line 5)
y=integrfn(A,x1,x2);
Can someone tell me the problem?
Thank you!!

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 采纳的回答

Star Strider
Star Strider 2017-11-10

0 个投票

The int function is part of the Symbolic Math Toolbox. The most appropriate function is integral, with the integrand as an anonymous function:
y = integral(@(x) A*exp(-x.^2).*cos(2*x)./(1+x.^2),x1,x2);

6 个评论
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Zhuoying Lin
Zhuoying Lin 2017-11-12
But it turns out that regardless of the input the output value is always o. Why?
Star Strider
Star Strider 2017-11-12
That is not the result I get:
A = 5;
x1 = 1;
x2 = 10;
y=integral(@(x) A*exp(-x.^2).*cos(2*x)./(1+x.^2),x1,x2)
y =
-188.9829e-003
I do not see any errors in your code that would lead that a result always being 0.
Zhuoying Lin
Zhuoying Lin 2017-11-12
The result is right only if I type the number and equation directly, yet if I run the whole script the result is always 0.
Star Strider
Star Strider 2017-11-12
This code works for me:
function [A,x1,x2]=value
A=input('Please enter a positive value: ')
x1=input('Please enter another positive value: ')
x2=input('Please enter a positive value that is greater than the previous one: ')
end
function y=integrfn(A,x1,x2)
y = integral(@(x) A*exp(-x.^2).*cos(2*x)./(1+x.^2),x1,x2);
end
[A,x1,x2]=value
y=integrfn(A,x1,x2)
fprintf('The value of the integral is %.3f', integrfn(A,x1,x2))
When I run it:
Please enter a positive value: 10
A =
10.0000e+000
Please enter another positive value: 1
x1 =
1.0000e+000
Please enter a positive value that is greater than the previous one: 5
x2 =
5.0000e+000
A =
10.0000e+000
x1 =
1.0000e+000
x2 =
5.0000e+000
y =
-377.9658e-003
The value of the integral is -0.378
Zhuoying Lin
Zhuoying Lin 2017-11-12
I figure out why now. Thank you!
Star Strider
Star Strider 2017-11-12
My pleasure!

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