Undefined function or variable 'betta'

Matlab just ignore the if else statement. I tried replacing betta with different words such as x3 but it is still the same. I am able to create alpha in the workspace but not betta. Is there any way for me to fix this problem?

Thank you.

Answer 1

[Walter Roberson]

You have

if (x2 < -28)
    betta = (-0.0002.*(x2)) + 2.0952
elseif (x2 >= -28) & (x2 < 54)
    betta = ((-8e-9).*((x2)^5)) + ((5e-7).*((x2)^4)) + ((1e-5).*((x2)^3)) + (0.0011.*((x2)^2)) - (0.0377.*(x2)) + 1.7084
elseif (x2 >= 54)
    betta = (-0.0001.*(x2)) + 0.002
end

but your x2 is a vector.

When you write

if (x2 < -28)

the meaning is the same as

if all(x2 < -28)

but some of your values are not less than -28, so the test fails. Then

elseif (x2 >= -28) & (x2 < 54)

is the same as

elseif all((x2 >= -28) & (x2 < 54))

and that fails because it is not true for some of the values. Then

elseif (x2 >= 54)

is the same as

    elseif all(x2 >= 54)

and that fails because it is not true for all of the values.

You either need to loop or to use logical indexing.

mask1 = (x2 < -28);
mask2 = (x2 >= -54);
mask3 = ~(mask1 | mask2);

betta(mask1) = (-0.0002.*(x2(mask1))) + 2.0952;
betta(mask2) = (-0.0001.*(x2(mask2))) + 0.002;
betta(mask3) = ((-8e-9).*((x2(mask3)).^5)) + ((5e-7).*((x2(mask3)).^4)) + ((1e-5).*((x2(mask3)).^3)) + (0.0011.*((x2(mask3)).^2)) - (0.0377.*(x2(mask3))) + 1.7084;

[CAL]

thank you very much!