Errors in my program with mpower and mtimes

I am writing a program to find conditional density functions for a transmitter going through Gaussian noise to receiver. In order to make plots for f(x|y) vs x given different values for y I need to have f be a piece wise function which I have shown below. These are the errors I am getting when trying to run my program.

??? Error using ==> mtimes Inner matrix dimensions must agree.

Error in ==> PartA at 6 k1 = int((x/(25*((8*3.14).^(1/2)))*(e.^((-(y-x).^2)/8))),x,0,5);

Here is my function and main program. If anyone knows what I am doing wrong please help.

i = 1;

y = -5;

e = 2.71;

x = 0 : 0.1 :10;

while(y <= 20)

k1 = int((x/(25*((8*3.14)^(1/2)))*(e^((-(y-x)^2)/8))),x,0,5);

k2 = int((0.4-(x/25))*(1/((8*3.14)^(1/2))*(e^((-(y-x)^2)/8))),x,5,10);

f = piecewise(x,y,k1,k2);

figure(i)

plot(x,f,'.');

y = y + 5;

i = i + 1;

end

function [ f ] = piecewise( x , y , k1, k2 )

e = 2.71;

if x > 0 && x <= 5

    f = ((1/k1) * (x/(25*((8*3.14)^(1/2))) * (e^((-(y-x)^2)/8))));

elseif x > 5 && x <= 10

    f = ((1/k2) * (0.4-(x/25)) * (1/((8*3.14)^(1/2))*(e^((-(y-x)^2)/8))));

else

    f = NaN;

end

end

Answer 1

[dpb]

Error in ==> PartA at 6 
k1 = int((x/(25*((8*3.14).^(1/2)))*(e.^((-(y-x).^2)/8))),x,0,5);

Looks like you're missing the 'dot' on the '.*' operator. You used it for the exponent, but unless you're intending doing a matrix multiplication of the vectors instead of element-by-element, you need it there, too.

Answer 2

[Cameron]

thanks for the quick feedback, but I have made this change multiple times and I end up getting a similar error message on the same line. I have edited my program to this and I am still getting strange error messages which are:

Error in ==> fun1 at 3 f1 = (x/(25*((8*3.14).^(1/2))) * (e.^((-(y-x).^2)/8)));

Error in ==> @(x)fun1(x,y)

Error in ==> quad at 76 y = f(x, varargin{:});

Error in ==> PartA at 5 k1 = quad(@(x)fun1(x,y),0,5);

i = 1;

y = -5;

e = 2.71;

while(y <= 20)

k1 = quad(@(x)fun1(x,y),0,5);

k2 = quad(@(x)fun2(x,y),5,10);

f = piecewise(x,y,k1,k2);

figure(i)

plot(x,f,'.');

y = y + 5;

i = i + 1;

end

-------------And fun1 and fun2 are as follows

function [ f1 ] = fun1( x , y )

e = 2.71;

f1 = (x/(25*((8*3.14).^(1/2))) * (e.^((-(y-x).^2)/8)));

end

function [ f2 ] = fun2( x , y )

e = 2.71;

f2 = (0.4-(x/25)) * (1/((8*3.14).^(1/2))*(e.^((-(y-x).^2)/8)));

end

[dpb]

Whatever changes you've made, you still didn't change the '*' to '.*' in

Error in ==> fun1 at 3 f1 = (x/(25*((8*3.14).^(1/2))) * (e.^((-(y-x).^2)/8)));

What are dimensions of x and y and what is the dimension of f1 intended to be?

[Star Strider]

I suggest putting ‘.’ in front of every *, / and ^ operator in a function unless you know you want to do matrix operations.