MATLAB: Attempted to access f(0); index must be a positive integer or logical

positive integer

function [ w ] = trap_wfp610( n )
% Calculates the work done using numerical integration and the trapezoidal rule
%   Detailed explanation goes here
h=(5*10^-2)/n;
a=0;
b=5*10^-2;
f=(5*(10^5)*a+10^5)*pi*(5*10^-2)^2
g=(5*(10^5)*b+10^5)*pi*(5*10^-2)^2
w=h/2*(f(a)+g(b))
end

Best Answer

You need to create these two lines as anonymous functions:

f = @(a) (5*(10^5)*a+10^5)*pi*(5*10^-2)^2
g = @(b) (5*(10^5)*b+10^5)*pi*(5*10^-2)^2

and you won’t get that error.

Related Solutions

MATLAB: This statement is not inside any function. (It follows the END that terminates the definition of the function “trap_wfp610”.)

Kevin, it's hard to tell what exactly you would like to do and what is going wrong. One thing you could do is do both computations within the same function and return all results:

 function [ w,Ws,error ] = trap_wfp610( n )
 % Calculates the work done using numerical integration and the trapezoidal rule
 % Detailed explanation goes here
 h = (5*10^-2)/n;
 a = 0;
 b = 5*10^-2;
 f = @(a)(5*(10^5)*a+10^5)*pi*(5*10^-2)^2;
 g = @(b)(5*(10^5)*b+10^5)*pi*(5*10^-2)^2;
 w = h/2*(f(a)+g(b));
 syms x 
 k1 = 500000 
 k2 = 10^5 
 p  = (k1*x+k2)*pi*.05^2 
 Ws = int(p,x,0,5*10^-2)
 error = abs((w-Ws)/Ws)*100;
 end

MATLAB: ??? Attempted to access f(0); index must be a positive integer or logical. Help me to solve this problem.

Thomas - see anonymous functions for details on how to properly define an anonymous function. Your code

 f = sin(x);

is valid if x is known, but if you wish to use it as a function as you are doing with

 Area = Area +(h/2)*(f(a) + f(a+h));

then you need to define f as

 f = @(x)sin(x);

Try the above and see what happens!

Best Answer

Related Solutions

MATLAB: This statement is not inside any function. (It follows the END that terminates the definition of the function “trap_wfp610”.)

MATLAB: ??? Attempted to access f(0); index must be a positive integer or logical. Help me to solve this problem.

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