In an assignment A(I) = B, the number of elements in B and I must be the same

hi,

I am facing problem with this code:

function P = legendre(x,n)  
  P(1) = 1;
  P(2) = x;
  P(3) = (3*(x^2)- 1)/2;
  P(n+1) =((2*(n+1))* x *(P(n)) - n*(P(n-1)))/(n+1); 
end

Ans Test_bech is:

clear legendre;
x = -1;
a = 5; 
len = length(x); 
P = zeros (1,len);
for i = 3:a
 P(n+1) = legendre(x,i);
end

when I run this test script. it will show this error:

In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in lendre_tb (line 11)

P(n+1) = legendre(x,3);

please help me out this!!

[yonatan gerufi]

i can't execute your code , in P(n+1) = ...

because n is not defines. can you write your full test script code?

[Mikhail]

The easiest way to eliminate this type of error - use debug mode. Set breakpoint at the line where error occurs, and before evaluating this line in debug mode check size() of left and right hand sizes.

[Varinder]

replace P(n+1) with

P(i)= legendre(x,3), try now

Answer 1

[the cyclist]

The specific reason you are getting this error is that the output of your legendre function is a vector, but in the line

P(n+1) = LP(x,i);

you are assigning that vector output to a single element of P.

[Varinder]

can I solve this by using:

P = zeros (1,5);

I think its a vector representation having five elements filled with 0.

but still I am getting the same error.

[Guillaume]

Regardless of the size of P, if n is scalar,

P(n+1)

is a scalar, i.e. a single number. You're trying to stuff a vector, i.e. several numbers in there. No matter how you try, it's not going to fit. You either need to change your legendre function to return a single number or put the output into more than one number.

[Varinder]

dear, now I am getting this error

Attempted to access P(4); index out of bounds because numel(P)=3.

Error in legendre (line 5) P(n+1) =((2*(n+1))* x (P(n)) - n(P(n-1)))/(n+1);

Error in new_tb (line 7)

i just modified my test script

clear legendre;

x = -1;

n=5;

 P = zeros (1,n);

for i = 3:n

     [P] =legendre(x,i); 

 end