undefined function inside two if statements

%Currently I have the code below and Y isn't returning any values. When I try displaying Y outside of the statements Matlab returns that Y is an undefined function.
%How can I output a value for Y? I'm sorry for the basic question, new to Matlab.
%X_1 is just a number and RoundedBoverT & RoundedBeta are matricies
if RoundedBoverT == 2
    if RoundedBeta == 0.5
        Y = 1.47*(X_1*X_1*X_1*X_1*X_1*X_1) - 5.5755*(X_1*X_1*X_1) + 7.8174*(X_1*X_1) - 4.9808*(X_1) + 1.8211;
        disp(Y)
    elseif RoundedBeta == 0.6
        Y = 7.373*(X_1*X_1*X_1*X_1*X_1*X_1) - 37.301*(X_1*X_1*X_1*X_1*X_1) + 75.133*(X_1*X_1*X_1*X_1) - 77.111*(X_1*X_1*X_1) + 43.138*(X_1*X_1) - 13.169*(X_1) + 2.454
        disp(Y)
    elseif RoundedBeta == 0.9
        Y = -1.5143*(X_1*X_1*X_1*X_1*X_1) + 7.4603*(X_1*X_1*X_1*X_1) - 14.377*(X_1*X_1*X_1) + 13.637*(X_1*X_1) - 6.232*(X_1) + 1.8101
       disp(Y)
    end
end

Answer 1

[David Hill]

Do not know what you want when you say if RoundedBoverT == 2 ...

if nnz(RoundedBoverT == 2)%do you mean any element of matrix ==2?
    if nnz(RoundedBeta == 0.5)%do you mean any element of matrix == .5?
        Y = 1.47*X_1^6 - 5.5755*X_1^3 + 7.8174*X_1^2 - 4.9808*X_1 + 1.8211%no ; will print value of y to work space
    elseif nnz(RoundedBeta == 0.6)
        Y = 7.373*X_1^6 - 37.301*X_1^5 + 75.133*X_1^4 - 77.111*X_1^3 + 43.138*X_1^2 - 13.169*X_1 + 2.454
    elseif nnz(RoundedBeta == 0.9)
        Y = -1.5143*X_1^5 + 7.4603*X_1^4 - 14.377*X_1^3 + 13.637*X_1^2 - 6.232*X_1 + 1.8101
    end
end

[Guillaume]

An even better way of writing this kind of expression would be:

Y = polyval([1.47, 0, 0, -5.5755, 7.8174, -4.9808, 1.8211], X_1);
%and so on...

[Joshua Prosper]

RoundedBoverT is a matrix and I want the if statement to use the correct equation depending on each value in the matrix

[David Hill]

Then do what with the calculations? Store them into matrix Y? I think this might be what you are looking for.

y=zeros(size(RoundedBoverT));
y(RoundedBeta(RoundedBoverT==2)==.5)=polyval([1.47,0,0,-5.5755,7.8174,-4.9808,1.8211],X_1);
y(RoundedBeta(RoundedBoverT==2)==.6)=polyval([7.373,-37.301,75.133,-77.111,43.138,-13.169,2.454],X_1);
y(RoundedBeta(RoundedBoverT==2)==.9)=polyval([-1.5143,7.4603,-14.377,13.637,-6.232,1.8101],X_1);

[Joshua Prosper]

thank you very much, i appologise for the poor explination, i havent fully figured out my logic yet

Answer 2

[Guillaume]

"RoundedBoverT is a matrix and I want the if statement to use the correct equation depending on each value in the matrix"

You need to loop over each element of RoundedBoverT:

Y = zeros(size(RoundedBoverT));  %always preallocate the output if you're filling it in a loop
for idx = 1:numel(RoundedBoverT)
    if RoundedBoverT(idx) == 2
        %I'm assuming that RoundedBeta is the same size as RoundedBoverT, you haven't said anything about it
        if RoundedBeta(idx) == 0.5  
            Y(idx) = polyval([1.47, 0, 0, -5.5755, 7.8174, -4.9808, 1.8211], X_1);
        elseif RoundedBeta == 0.6
            Y(idx) = polyval([7.373, -37.301, 75.133, -77.111, 43.138, -13.169, 2.454], X_1);
        elseif RoundedBeta == 0.9
            Y(idx) = polyval([0, -1.5143, 7.4603, -14.377, 13.637, -6.232, 1.8101], X_1);
        else
            %never end on an elseif
            %what to do when it's neither 0.5, 0.6 or 0.9
            error('case undefined');
        end
    else
        %what to do when it's not 2?
        error('case undefined');
    end
end

Note that your tests involves exact equality. Be aware that:

>> (0.1 + 0.1 + 0.1) == 0.3
ans =
  logical
   0

is false in matlab due to floating point precision. That's another topic altogether.