MATLAB: Output argument “T” (and maybe others) not assigned during call to “temp_alt” error

errorerror output functionMATLABnot assigned during calloutputoutput argumentscript

I am using one function that calls using two others. Here are the functions.
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function mach_number=mach(V);
mach_number=(V.*10.^3)./(sqrt(1.40.*287.*(temp_alt(alt_velo(V)))));
end
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function alt=alt_velo(V);
alt=((.0389*V.^5)-(.8115*V.^4)+(6.537*V.^3)-(25.45*V.^2)+(53.425*V)+3.8234)*(10.^3);
end 
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function T=temp_alt(h);
if (h >= 25000)
    T=(-131.21+.00299.*h)+273.15;
elseif (11000 < h) & (h < 25000);
    T=(-56.46+273.15);
elseif    (h <= 11000);
    T=(15.04-(.00649.*h))+273.15;
end
end
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The function mach works when I enter mach(1:1:10) in the command window but when I do mach(.001:.001:1) I get the error below, I do not understand why. Please help.
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Error in temp_alt (line 12)
if (h >= 25000)
Output argument "T" (and maybe others) not assigned during call to "temp_alt".
Error in mach (line 12)
mach_number=(V.*10.^3)./(sqrt(1.40.*287.*(temp_alt(alt_velo(V)))));

Best Answer

You are passing a vector in to temp_alt but you are treating the argument as if it is a scalar.
You should be using logical indexing rather than if/elseif/else
function T=temp_alt(h);
  T = zeros(size(h), class(h));
  idx1 = h >= 25000;
  T(idx1) = (-131.21 + .00299.*h(idx1)) + 273.15;
  idx2 = (11000 < h) & (h < 25000);
  T(idx2) = -56.46 + 273.15;
  idx3 = ~(idx1 | idx2);
  T(idx3) = (15.04 - (.00649.*h(idx3))) + 273.15;
end
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