Problem in if-else if-else structure

Question

KalMandy 2016-11-11

0
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https://ww2.mathworks.cn/matlabcentral/answers/311793-problem-in-if-else-if-else-structure

评论： KalMandy 2016-11-11

Hi, I have written the following program. But it does not output the result I get from manual calculations. Perhaps I have gone wrong in writing the logic. The program is as below.

if X1(i)==a(i) && X2(i)==b(i)
t(i)= a(i)* b(i);
    else if X1(i)== a(i) && X2(i)==NaN && X1(i+1)==a(i+1) && X2(i+1)==NaN
      t(i)= a(i)* a(i+1);            
    else if X1(i)== a(i) && X2(i)==NaN && X1(i+1)==NaN && X2(i+1)==b(i+1)
            t(i)= a(i)* b(i+1);
    else if X1(i)==NaN && X2(i)== b(i)&& X1(i+1)==a(i+1) && X2(i+1)==NaN
            t(i)= b(i)* a(i+1);
        else if X1(i)==NaN && X2(i)== b(i)&& X1(i+1)==NaN && X2(i+1)==b(i+1)
                t(i)= b(i)* b(i+1);
            else
               t(i)= 0; 
        end
        end
        end
        end   
    end

The input is as below. X1=NaN a(2) NaN a(4) a(5) NaN NaN

X2= NaN b(2) b(3) NaN b(5) NaN NaN

i=1:7 and i=8 equals to i=1

The output is as below.

t= 0 c 0 0 d 0 0

But there should be output at t(3) and t(4). Can anybody point out where I went wrong? Thanks

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KalMandy 2016-11-11

Should I be using a 'switch' in this case? I am new to matlab and have never used 'switch' before. Can someone please help?

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Answer 1

James Tursa 2016-11-11

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311793-problem-in-if-else-if-else-structure#answer_242979

编辑：James Tursa 2016-11-11

在 MATLAB Online 中打开

You can't compare to NaN with the == operator, since NaN is not equal to anything (including itself). You must use the isnan function. E.g.,

else if X1(i)== a(i) && X2(i)==NaN && X1(i+1)==a(i+1) && X2(i+1)==NaN

should be

else if X1(i)== a(i) && isnan(X2(i)) && X1(i+1)==a(i+1) && isnan(X2(i+1))

etc.

For example,

>> a = nan
a =
   NaN
>> a == nan
ans =
     0
>> a == a
ans =
     0

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KalMandy 2016-11-11

my code is long and I only showed the part where I assume the problem is. I can post it, but I assume that would confuse you. But here it is. I have substituted X1=onpointX1, X2=onpointX2 etc.

KalMandy 2016-11-11