User-Defined function to add polynomials

function p= polyno(p1,p2,operation)
%Write a user-defined function that adds are substract polynomials of any two orders

len_p1=length(p1);
len_p2=length(p2);
 if len_p1 > len_p2
     tmp=[zeros(1:len_p1-len_p2),p2];
     p2=tmp;
 elseif len_p1 < len_p2  
     tmp=[zeros(1:len_p2-len_p1),p1];
     p1=tmp;
 end 
 
 if operation == 'Add'
     p = p1 + p1;
 elseif operation == 'Subtract'
     p = p1 - p2;
     
 else 
     error('Must enter "Add" or "Subtract" to complete operation')
 end 
end 
    

I know there is a lot of problems witht the code, but the main problems is that it wont add diffrent ordered polynomials correctly, and also it doesnt let me subtract polynomials, it tells me theres an error with the line of the code that tells it to add. How would I go about fixing this?

[Walter Roberson]

You should use strcmp not ==

[Walter Roberson]

Hint: zeros can be called with a difference between lengths. If the difference is positive then zeroes will be creating an appropriate padding. If the difference in length is 0 or negative then zeros will not give an error message and will silently create empty padding. If you think about this you will see that you do not need to tests the relative length first: you can just go ahead and pad and everything will turn out the right size.

[Jose De La Pena]

I'm not too entirely sure what "padding" means.

[Jose De La Pena]

Additionally, I thought I already encounted for the zeroes with adding extra ones for the difference between the length of the two polynomials.

[Walter Roberson]

Remember that zeros(1:5) is the same as zeros([1,2,3,4,5]) which creates a n array that is 1 * 2 * 3 * 4 * 5