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undefined function inside two if statements

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Joshua Prosper
Joshua Prosper 2020-2-27
关闭： MATLAB Answer Bot 2021-8-20
%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

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回答（2 个）

David Hill
David Hill 2020-2-27
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
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显示 2更早的评论
David Hill
David Hill 2020-2-27
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
Joshua Prosper 2020-2-27
thank you very much, i appologise for the poor explination, i havent fully figured out my logic yet
Guillaume
Guillaume 2020-2-27
"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.

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