Problem of Interpolation in matlab

Question

addou abdeljalil 2015-7-9

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https://ww2.mathworks.cn/matlabcentral/answers/229205-problem-of-interpolation-in-matlab

回答： addou abdeljalil 2015-7-9

Hi, My problem are like this: i have a 2 colons of 178 values define UM (Unity Monitor) and angles and i wish to compare one other angle extracted from image dicom to this angle in order to find UM corresponding. i tried interpolation but it doesn't work

    % code
   UM        angle  
   0         0.5000
   1.4700    1.2300
   4.3700    3.2800
   7.2900    5.2800
for example, if i have angle = 4° what is value of UM corresponding ?

Any help will be appreciate

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Answer 1

Azzi Abdelmalek 2015-7-9

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https://ww2.mathworks.cn/matlabcentral/answers/229205-problem-of-interpolation-in-matlab#answer_185545

编辑：Azzi Abdelmalek 2015-7-9

在 MATLAB Online 中打开

    A=[0         0.5000
       1.4700    1.2300
       4.3700    3.2800
       7.2900    5.2800]
UM=A(:,1)
angle=A(:,2)
UMi=4
anglei=interp1(UM,angle,UMi)

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addou abdeljalil 2015-7-9

编辑：Azzi Abdelmalek 2015-7-9

Thank you Azzi for your answer. your answer works well for 4 but when I test other larger values it recturn me not correct values. in fact I have two columns that are each 178 lines so when test for example angle = 182° it return me UM = 287 but the reel value is 126.11.

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Answer 2

addou abdeljalil 2015-7-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/229205-problem-of-interpolation-in-matlab#answer_185570

在 MATLAB Online 中打开

I tested this code but there also some pb.

 for i = 1:178 
         if A(i,2)< angle < A(i+1,2)
                 UM = interp1(A(i,1),A(i+1,1),angle) 
         end      
 end
it return me this error : Error using interp1 (line 182)
There should be at least two data points.