Output argument "v" (and maybe others) not assigned during call to "Deflection_vmndangi".

function [v] = Deflection_vmndangi(x)
% Author : Vainquer Ndangi
% Date : September 22, 2019
% Purpose : Calculationg Deflection
% Inputs:
% x: position
% Outputs:
% v : Deflection
if (x > 0 & x <= 120)
    v = (1./(3.19 .* 10.^9)) .* (800 .* x.^3 - 13.68 .* 10.^6 .* x - 2.5 .* x.^4);
end
if (x > 120 & x <= 240)
    v = (1./(3.19 .* 10.^9)) .* (800 .* x.^3 - 13.68 .* 10.^6 .* x - 2.5 .* x.^4 + (25 .* (x - 120).^4));
end
if (x > 240 & x <= 360)
    v = (1./(3.19 .* 10.^9)) .* (800 .* x.^3 - 13.68 .* 10.^6 .* x - 2.5 .* x.^4 + (25 .* (x - 120).^4) + (600 .* (x - 240).^3));
end
 
end

every time i run this function with a single value it works. However, when i try to run it with a vector it only works if every element of the vector are under the same condition. if one element is not it will return "Output argument "v" (and maybe others) not assigned during call to "Deflection_vmndangi".". what can i do?

Answer 1

[dpb]

None of the conditions will be met if you pass a vector as you have written the IF tests. IF is true iff (if and only if) all elements of the logical vector that results from the comparison are true--if you pass a vector of arguments that don't all satisfy the same condition, at least one member of that test will be false for every case and so lacking an "else" clause or assignment for that case, the output v is never assigned.

You need something like

function [v] = Deflection_vmndangi(x)
% Author : Vainquer Ndangi
% Date : September 22, 2019
% Purpose : Calculationg Deflection
% Inputs:
% x: position
% Outputs:
% v : Deflection

  v=zeros(size(x));
  ix=(x>0 & x<=120);
  v(ix) = (800*x(ix).^3 - 13.68E6*x(ix) - 2.5*x(ix).^4)/3.19E9 ;
  ix=(x > 120 & x <= 240);
  v(ix) = (800*x(ix).^3 - 13.68E6*x(ix) - 2.5*x(ix).^4 + 25*(x(ix)-120).^4)/3.19E9;
  ix=(x>240 & x<=360);
  v(ix) = (800*x(ix).^3 - 13.68E6*x(ix) - 2.5*x(ix).^4 + 25*(x(ix)-120).^4  + 600*(x(ix)-240).^3)/3.19E9;
end

so that each element is computed by the given correlation.

See the doc for if and for "logical indexing" for more details.

NB: the "dot" operators are not needed for multiplication by a constant and it's much more efficient to write the coefficient magnitude as a literal constant rather than computing the powers of 10.

[Vainqueur Ndangi]

i tried it like you proposed but it did not work. i was getting a vector of zeros. thanks for the effort.

[dpb]

Show your work...it'll work. Probably the zeros were that I see I missed a trailing semicolon on the last computation of the logical indexing vector. I'll fix that in the Answer now...

ADDENDUM/ERRATUM

Ah! I forgot to put the indexing vector ix on the LHS assignment so overwrites the whole vector every time. Fixed that, too...

ADDENDUM SECOND

Note there will be no assignment other than the initialization for any input outside [>0 360] and there's also no error checking to warn or error on such.

[Vainqueur Ndangi]

Works perfect. Thank you so much!

[dpb]

Slightly more efficient, maybe...

function [v] = Deflection_vmndangi(x)
% Author : Vainquer Ndangi
% Date : September 22, 2019
% Purpose : Calculationg Deflection
% Inputs:
% x: position
% Outputs:
% v : Deflection
  v = (800*x.^3 - 13.68E6*x - 2.5*x.^4)/3.19E9 ;
  ix=(x > 120 & x <= 240);
  if any(ix)
    v(ix) = V(ix) + 25*(x(ix)-120).^4/3.19E9;
  end
  ix=(x>240 & x<=360);
  if any(ix)
    v(ix) = v(ix) + 600*(x(ix)-240).^3/3.19E9;
  end
end

Still no testing of bounds on inputs but only does the sections needs to.