How can I display an error message in MATLAB?

I was doing a model for a slider-crank mechanism and I wanted to display an error for when the crank's length exceeds that of the slider arm. With the crank's length as r2 and the slider's as r3, my code went like this:

if r3=<r2
    error('The crank's length cannot exceed that of the slider')
end

I get the error:

???     error('The crank's length cannot exceed that of the slider')
         开发者_如何学运维                |
Error: Unexpected MATLAB expression.

can someone tell me what I'm doing wrong and how to fix it please?

When you want to use the ' character in a string, you have to precede it with another ' (note the example in the documentation):

if (r3 <= r2)
  error('The crank''s length cannot exceed that of the slider');
end

Also, note the change I made from =< to <=.

You can print to the error handle as well:

fprintf(2,'The crank''s length cannot exceed that of the slider');

I believe the comparison operator should be <= not the other way around, unless that was only a typo in your question

Also you should escape the ' character using ''