Error using * (Inner matrix dimensions must agree)

This is what I have so far

if true
clear all; 
clc;
close all;
t=(-.5:1*exp(-6):2);
f=6*exp(-1.5*t)*cos(8*3.14*t);
F=input('Enter a particular value for f(t): ');
Figure 1;
Plot (f,t,'r',F,t,'g');
grid on;
hold on;
end

I know my problem is at the f= line, what am I doing wrong with the *? Thanks

Answer 1

[dpb]

doc times % or '.*'

will answer all...

Answer 2

[Dan]

Thanks guys, for the same code I need to determine the number of times f(t) crosses the line y(t)=F using a while- end statement.

f(t) being f=6*exp(-1.5*t).*cos(8*3.14*t); and F being the input from the user.

I am not really sure how to write this? Pretty sure I am over thinking it.

Answer 3

[Matt J]

f=6*exp(-1.5*t).*cos(8*3.14*t);

Answer 4

[Dan]

Can I do something like

if true%
x = f;               
while x >= F        
   disp(x)
   x = x + 1;  
end

[dpb]

Not quite...the initialization sets x to the full vector of f so the while will be a vector and if F is > any value at all in f the condition will never evaluate to T.

Is it mandatory to use while? If not, consider what

diff(x>=F)

yields and how one might use something of that nature.

Note that in your sample loop, even if you set

x=f(1);

as the initialization the while doesn't work as you need and even if it did it doesn't find the crossing points.