if elseif giving too many outputs

Hi everyone, I'm trying to finish writing a matlab code that will read an input for a certain altitude, and then calculate a couple of properties based on that altitude. The thing is, for each range of altitude, the values for the variables used in calculating these properties changes, so I have to reassign each variable new values based on the range this input falls under.

Here is my code:

 if (H <= 11000)
    Hbi = 0;
    deltai = 1;
    KTi = -6.5;
    Tbi = 288.15;

    LinP = (deltai.*(1+((KTi/Tbi).*(H-Hbi))).^(expterm/KTi));
    ConstP = (deltai.*exp(-((expterm)/Tbi).*(H-Hbi)));
    fprintf('Linear pressure ratio = %f\n', LinP);

 elseif (H < 20000)
    Hbi= 11000;
    deltai = 0.22336;
    KTi = 0;
    Tbi = 216.65;

    LinP = (deltai.*(1+((KTi/Tbi).*(H-Hbi))).^(expterm/KTi));
    ConstP = (deltai.*exp(-((expterm)/Tbi).*(H-Hbi)));
    fprintf('Linear pressure ratio = %f\n', LinP);

 end

Please note that "expterm", etc. has already been established, so that's not my issue. There is no error when I run it. When I run it, it asks for the input, and when I put in the input, it gives me like ten thousand different values.

Answer 1

[Image Analyst]

That's because LinP is an array of like ten thousand elements, and this:

fprintf('Linear pressure ratio = %f\n', LinP);

will repeat for every one of those ten thousand elements. LinP is 10,000 values because either H or expterm is 10,000 values.

[Walter Roberson]

Note that if H is a vector, then

   if (H <= 11000)

is the same as

   if all(H(:) <= 11000)

which would be false if even one value of H > 11000.

[Stenila Simon]

So how would I change it to just evaluate which range the input H lies in and execute the function?

Answer 2

[Walter Roberson]

    LinP = nan(size(H));
    ConstP = nan(size(H));

    mask = H <= 11000;

    Hbi = 0;
    deltai = 1;
    KTi = -6.5;
    Tbi = 288.15;

    LinP(mask) = (deltai.*(1+((KTi/Tbi).*(H(mask)-Hbi))).^(expterm/KTi));
    ConstP(mask) = (deltai.*exp(-((expterm)/Tbi).*(H(mask)-Hbi)));

    mask = H > 11000 & H < 20000;

    Hbi= 11000;
    deltai = 0.22336;
    KTi = 0;
    Tbi = 216.65;

    LinP(mask) = (deltai.*(1+((KTi/Tbi).*(H(mask)-Hbi))).^(expterm/KTi));
    ConstP(mask) = (deltai.*exp(-((expterm)/Tbi).*(H(mask)-Hbi)));

    plot(H, LinP)

You did not have a final "elseif" giving a value for the situation where H was not in either range, so I assigned NaN for that case.