Error: Array indices must be positive integers or logical values. / no indices in code

Hello,

When running my code I get multiple errors but the error seems to be with a misusage of indices.

My code:

syms P R;

B = 6;

r = @(P) 0.5 * (B - P)^(-0.5);

R_star = @(P) r * P;

R_max = 6;

R_dist = 1 / 6;

c_prime = @(x) x;

expectation = int(@(R) R * R_dist, R, R_star, R_max);

one_minus_cdf = int(@(R) R_dist, R, R_star, R_max);

RHS = @(P) (expectation(P) - c_prime(1)) / (r(P) * one_minus_cdf(P));

to_be_min = @(P) (P - RHS(P))^2;

x0 = 0;

bubble_price = fminsearch(to_be_min, x0);

The errors:

Array indices must be positive integers or logical values.

Error in sym/subsref (line 909)

R_tilde = builtin('subsref',L_tilde,Idx);

Error in

attempt_code_bubble>@(P)(expectation(P)-c_prime(1))/(r(P)*one_minus_cdf(P))

(line 13)

RHS = @(P) (expectation(P) - c_prime(1)) / (r(P) * one_minus_cdf(P));

Error in attempt_code_bubble>@(P)(P-RHS(P))^2 (line 15)

to_be_min = @(P) (P - RHS(P))^2;

Error in fminsearch (line 201)

fv(:,1) = funfcn(x,varargin{:});

Error in attempt_code_bubble (line 18)

bubble_price = fminsearch(to_be_min, x0);

Thank you for your help!

Answer 1

[Walter Roberson]

R_star = @(P) r * P;

r is a function handle. You cannot multiply a function handle by a value. You can invoke the function handle and multiply the results.

expectation = int(@(R) R * R_dist, R, R_star, R_max);

That would give you a symbolic expression as a result, not a function

RHS = @(P) (expectation(P) - c_prime(1)) / (r(P) * one_minus_cdf(P));

That would try to index the symbolic expression at the input P. If P were symbolic you would get the error message you are seeing.