If...elseif Statement Not Pulling Variables

Question

Fun Dan 2015-4-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/196274-if-elseif-statement-not-pulling-variables

评论： Fun Dan 2015-4-6

Please I need help. I am trying to run the following arguments for three different cases using the if..elseif statement but it is popping up errors. I am trying to pull the values for the variables a, b and c for a subsequent calculation, depending on what statement is true from the three cases below.

if (E<0.01) and (F<L1) or (E>0.01) and (F<L2) 
then 
   a = 0.98; b = 0.4846; c = 0.0868;
elseif (0.01<E<0.4) and (L3<F<L1) or (E>0.4) and (L3<F<L4)
then 
   a = 0.845; b = 0.5351; c = 0.0173;
elseif (E<0.4) and (F>L1) or (E>0.4) and (F>L4)
then 
  a = 1.065; b = 0.5824; c = 0.0609;
end

Thank you

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Jan 2015-4-6

I've formatted your code, do improve the readability. Please apply a proper code formatting by your own - thanks!

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Answer 1

Stephen23 2015-4-6

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/196274-if-elseif-statement-not-pulling-variables#answer_174087

编辑：Stephen23 2015-4-6

在 MATLAB Online 中打开

That syntax is not MATLAB syntax at all: MATLAB if does not use a then statement, and while and and or do exist as functions, they cannot be used like that (only as functions, as the documentation clearly shows). It is also not possible to make two logical comparisons simultaneously, so 0.01<E<0.4 will always be an error.

You need to learn about basic MATLAB syntax and learn to read the documentation (read the links that I gave). These tutorials are a good place to start to learn MATLAB:

http://www.mathworks.com/help/matlab/getting-started-with-matlab.html

Here is a version that works without errors, as long as all of the input values are scalars:

if  (E<0.01 && F<L1) || (E>0.01 && F<L2)
    a = 0.98;
    b = 0.4846;
    c = 0.0868;
elseif (0.01<E && E<0.4 && L3<F && F<L1) || (E>0.4 && L3<F && F<L4) 
    a = 0.845;
    b = 0.5351;
    c = 0.0173;
elseif (E<0.4 && F>L1) || (E>0.4 && F>L4)
    a = 1.065;
    b = 0.5824;
    c = 0.0609;
end

Note that if none of these conditions are met, then these variables will not be defined! (and ergo an else statement might be a good idea).

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Stephen23 2015-4-6

编辑：Stephen23 2015-4-6

在 MATLAB Online 中打开

@Fun Dan: How are you calling this? When you write that the "output was 'FlowMod'", what is this the output of? Please show us the exact code that you use to call this script, either as text or in screenshot.

And please, as Image Analyst has already asked, format your code so that it is readable. You can use the {} Code button above the textbox to do this.

After I formatted your code correctly and replaced all of the || operators that you had rather mysteriously removed from the code, it worked just fine. I simply placed this in an Mfile called "temp":

% Parameters
V = 0.002;
D = 0.05021;
QL = 0.0033;
QG = 0.0033;
% Calculation of Correlation Parameters
F = 0.102*V^2/D;
E = QL/(QL+QG);
% Calculation of Non-Dimensional Numbers
L1 = 316* E^0.302;
L2 = 0.0009252*E^-2.4684;
L3 = 0.1*(E)^-1.4516;
L4 = 0.5*(E)^-6.738;
% Determination of Pressure Regime 
if (E<0.01 && F<L1) || (E>0.01 && F<L2)
    a = 0.98;
    b = 0.4846;
    c = 0.0868;
elseif (0.01<E && E<0.4 && L3<F && F<L1) || (E>0.4 && L3<F && F<L4)
    a = 0.845;
    b = 0.5351;
    c = 0.0173;
elseif (E<0.4 && F>L1) || (E>0.4 && F>L4)
    a = 1.065;
    b = 0.5824;
    c = 0.0609;
end
A = a*E^b/F^c;