how do i salve this?

[Walter Roberson]

That problem cannot be solved in MATLAB.

https://www.mathworks.com/matlabcentral/answers/38787-what-can-be-programmed-without-any-built-in-functions?s_tid=srchtitle

Answer 1

[David Hill]

I assume you cannot use the built-in function movsum()

 movsum(x,3,'Endpoints','discard');

But should be able to use other functions.

prs3=[];
for k=1:length(x)-2
    c=0;
    for m=0:2
        c=c+x(k+m);
    end
    prs3(k)=c;
end

[Walter Roberson]

prs3=[];

Literal [] appears to be a syntactic construct with the [] not executed to produce an empty array. The above line indeed does not execute any defined function.

for k=1:length(x)-2

That executes the built-in functions length() and minus() and colon() . However, for itself and what is written as an assignment do not execute any defined function.

    c=0;

Numeric values are constructed at parse time rather than at execution time, and non-subscripted assignment does not execute any defined function.

    for m=0:2

Numeric functions are constructed at parse time, and for itself does not involve executing any defined function. However, that involves executing the function colon()

        c=c+x(k+m);

That involves executing the function plus() and subsref() and plus()

    end

No defined function for that line

    prs3(k)=c;

That involves executing the function subsasgn()

end

No defined function for that line.

List of prohibitted functions executed:

• colon
• length
• minus
• plus
• subsasgn
• subsref

[Walter Roberson]

The requirement to not use any built-in MATLAB functions does not merely make the task difficult: it makes it impossible.