Matlab confuses variable with matrix

So I declare my function as: f=@(x) 54*(x^6) + 45*(x^5) - 102*(x^4) - 69*(x^3) + 35*(x^2) + 16*x - 4 and I get these errors:

Error using ^ (line 51)

Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To perform elementwise matrix powers, use '.^'.

Error in Bisection2>@(x)54*(x^6)+45*(x^5)-102*(x^4)-69*(x^3)+35*(x^2)+16*x-4 (line 6)

f=@(x) 54*(x^6) + 45*(x^5) - 102*(x^4) - 69*(x^3) + 35*(x^2) + 16*x - 4

Answer 1

[Star Strider]

Apparently, ‘x’ is a vector (or array). Use element-wise exponentiation (.^) in that event:

f=@(x) 54*(x.^6) + 45*(x.^5) - 102*(x.^4) - 69*(x.^3) + 35*(x.^2) + 16*x - 4

See: Array vs. Matrix Operations for an extended discussion.

[Christina Mil]

I did that and now I get the same error for the ' * ' operator. I replaced the function with:

f=@(x) 54.*(x.^6) + 45.*(x.^5) - 102.*(x.^4) - 69.*(x.^3) + 35.*(x.^2) + 16.*x - 4;

because the error says so :Error using *

Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise

multiplication, use '.*'.

However the error keeps coming up even after the .*

[Walter Roberson]

Your f is being passed a vector in a context where the surrounding code expects a scalar.

If you are writing typical bisection code you probably have something like

if f(a)*f(b) < 0

That code would be incorrect for the case where a and b are vectors.

I speculate that you are trying to keep track of all of the a and b values in vectors but forgot to index them to only get the current ones when you call f

[Star Strider]

@Walter — Thank you!

(There were no multiplications in the original Question.)