If...elseif Statement Not Pulling Variables

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

[Jan]

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

Answer 1

[Stephen23]

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).

[Fun Dan]

Thank you Stephen for your prompt response. I really appreciate it. I am actually new with Matlab and the link you sent is very helpful. I have tried to run the codes you just gave me. However, I am not able to calculate A = (a*C^b)/F^c based on the output from the code.

[Stephen23]

"not able to calculate" is not enough information: are you getting a wrong value, or an error message (in red), or a warning message, or did your laptop catch fire? Unless you tell us exactly what code you are running (with the values) and the complete and exact error messages that you might be getting, then it is impossible to know what might be preventing the calculation. Sorry, but we can't read minds!

[Fun Dan]

% 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;

The output I got was 'FlowMod' which is the name I used in saving the mfile.

[Image Analyst]

Read this, so we can read your code.

[Stephen23]

@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;

And ran the script from the command line like this:

>> temp

and checked the final value too

>> A
A =
     1.9372

[Fun Dan]

Thank you Stephen! It worked perfectly now. I got A = 1.9372 as well.