Function with subfunction inside

The function func takes any real array A as input and outputs an array B of equal size, whose entries are equal to twice the corresponding entry of A for every nonnegative entry of A, and equal to a given number n, for every negative entry of A. The function func accepts a subfunction subf. Complete the code in func and subf, as necessary.

function B=func(A,n)
% Replace A by B such that each entry of B equals:
% twice the entry of A if that entry of A is non-negative
% or n if the entry of A is negative
B = 2*subf(_______________ % COMPLETE THE ARGUMENT LIST
function C = subf(__________________ % COMPLETE THE
% ARGUMENT LIST
% subfunction of func
C___________________________________ % COMPLETE THE LINE

I am totally confused on this problem. With so few lines of code, how do I get it to distinguish whether the entry of A is negative or nonnegative.

I guess I would be

B = 2*sub(A)
C = subf(A<0,n)
C = n

Answer 1

[Image Analyst]

You need to use logical indexing to figure out where A is positive. For example

positiveValueLocations = A > 0; % Vector of 0's and 1's.

Now you can set those locations to twice the value

B=A; % Initialize
B(positiveValueLocations) = 2 * A(positiveValueLocations);

That's enough hint. Look up logical indexing if you want to know more. It should be trivial to set B = n for the other locations. There are two ways to do it: one by initializing to n and another by assigning values that aren't positiveValueLocations to n. I don't see any need whatsoever for any subfunction or for a variable C.

[Rick]

How does that fit into the framework of that problem? They want me to fill in the underline part

[Image Analyst]

Well it's kind of stupid, but to do it that dumb way you'd have to pass in A and ninto subf(), then do what I say to pass back A but with n/2 wherever A<=0. So C = A but with elements of A = n/2 wherever A<=0.