Reverse 2D-lookup Table

Question

Owen 2011-8-1

3
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12809-reverse-2d-lookup-table

评论： Michael Goebel 2023-10-4

I am having a lot of difficulty implementing this typ of controller in simulink.

To put it simply have a 2d-Lookup table a basically want to reverse engineer it. The 2d-lookup table takes in two input A and B and interpolates the corresponding output C in a large 79x101 matrix. I wish to define the output variable C for a fixed input variable A and find the corresponding variable B.

         _____________
    A--->|           |
         |2d-Looukup |--->C
    B--->|___________|
         ____________
    C--->| Reverse   |
         |  lookup   |--->B
    A--->|___________|

What I have been attempting is to focus on first is the input A. So lets say for example that I have the following matrix.

          0.4  0.5  0.6  0.7  (B)
         ____________________
     17.9|67   89   95   108
 (A) 18.0|74   92   110  123
     18.1|80   97   115  127
     18.2|84   106  119  135
                 (C)
                 

I have an input of 18.046 for the input A. Now matlab will interpolate between 18.0

and 18.1 to give me the following output.

         0.4  0.5  0.6  0.7  (B)  
         ___________________
 (A)8.046|76  94   112  125
                 (C)

So with the matrix output as shown below I define my desired output variable, e.g. C = 105. I then pass this variable C into a lookup table and matlab will interpolate the corresponding input variable B.

            0.4 0.5  0.6  0.7
            __________________
(C) 105--->|76  94  111  125| ---> 0.57  (B)

Could anyone help me in acheieving this problem as I have been stuck on it for quite some time now. Much appreciated

Owen

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marouan akhabbil 2022-3-16

Hello

i had the same issue i wanted to inverse a 2D lookup table, i tried the formula in the previous comments but it gives NAN values so i creted my own formula, it's so simple based on one interpolation :

here is my script

clc

nbrC1 = 3 ; %nombre d'elelements desiré dans le vecteur C1

A=[1 2 ];

B=[1 2 ];

C=[2 3 ; 3 4 ];

%objectif passer de : entrée sont A et B à entrées A et C

%calcul de la matrice B1 et des deux lignes A1 et C1

%A1=A inchangé

%etape 1 : les elements de la ligne C1

minC=min(min(C));

maxC=max(max(C));

precision=(maxC-minC)/(nbrC1-1) ;

C1=minC:precision:maxC ;

nA= size(A) ;

nA= nA(2) ;

nC1= size(C1) ;

nC1= nC1(2) ;

% etape 2 les valeurs de B1 ( matrice )

B1=zeros(nA,nC1);

for i= 1:nA

tmpC=C(i,:);

for j = 1:nC1

B1(i,:)=interp1( tmpC,B,C1, 'spline', 'extrap');

end

% the result

%B1

%C1

%A1 = A

%Marouan AKHABBIL

Michael Goebel 2022-9-2

This script works well, but not for me: A has a size of 8, B has a size of 32.

I set nbrC1 = 8

But it doesnt woork for me: C1 has weird values

How can i fix this?

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Answer 1

Fangjun Jiang 2011-8-7

8
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12809-reverse-2d-lookup-table#answer_18111

在 MATLAB Online 中打开

For a given value of A1 and C1, you should be able to find the corresponding value B1. Do a two-loop iteration on different values of A and C, you should be able to reverse engineer the lookup table.

A=[17.9 18.0 18.1 18.2]';   
B=[0.4  0.5  0.6  0.7];
C=[67   89   95   108
   74   92   110  123
   80   97   115  127
   84   106  119  135];
A1=18.046;
%Z=interp2(A,B,C,A1,B);
Z=interp2(A,B,C',A1,B);
C1=105;
B1=interp1(Z,B,C1);

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Michael Goebel 2022-9-5

Thats a good question.

Here is my raw-Data:

A = [0.5:0.5:16]';

B = [-20,-10,0,25,40,60,80,100]';

C = reshape([0.142,0.234,0.325,0.417,0.508,0.599,0.69,0.781,0.872,0.963,1.054,1.145,1.235,1.326,1.417,1.508,1.598,1.689,1.779,1.87,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,0.173,0.265,0.356,0.447,0.539,0.63,0.72,0.811,0.902,0.993,1.083,1.174,1.265,1.355,1.445,1.536,1.626,1.716,1.806,1.896,1.987,2.08,2.173,2.265,2.358,2.451,2.543,2.636,2.731,2.827,2.924,3.021,0.301,0.393,0.483,0.574,0.664,0.753,0.843,0.932,1.022,1.114,1.206,1.299,1.395,1.491,1.587,1.683,1.781,1.879,1.977,2.076,2.176,2.275,2.375,2.474,2.573,2.673,2.773,2.873,2.973,3.072,3.172,3.271,0.318,0.608,0.694,0.78,0.865,0.951,1.038,1.129,1.221,1.314,1.408,1.503,1.597,1.692,1.788,1.883,1.978,2.072,2.167,2.262,2.357,2.451,2.545,2.638,2.732,2.826,2.919,3.011,3.104,3.196,3.288,3.379,0.313,0.612,0.898,1.172,1.339,1.393,1.452,1.515,1.58,1.646,1.712,1.78,1.848,1.916,1.985,2.054,2.123,2.193,2.263,2.334,2.406,2.477,2.55,2.623,2.696,2.77,2.844,2.918,2.992,3.067,3.142,3.217,0.31,0.599,0.871,1.129,1.376,1.513,1.554,1.6,1.649,1.7,1.753,1.807,1.863,1.92,1.978,2.038,2.1,2.163,2.227,2.292,2.359,2.426,2.495,2.564,2.634,2.704,2.776,2.848,2.92,2.993,3.067,3.142,0.3,0.564,0.808,1.043,1.278,1.516,1.631,1.658,1.689,1.723,1.761,1.803,1.849,1.899,1.952,2.007,2.064,2.124,2.186,2.249,2.314,2.38,2.448,2.517,2.587,2.658,2.73,2.803,2.877,2.951,3.026,3.102,0.29,0.538,0.773,1.011,1.254,1.501,1.67,1.689,1.713,1.742,1.777,1.817,1.861,1.908,1.959,2.013,2.069,2.128,2.188,2.251,2.316,2.382,2.45,2.519,2.588,2.659,2.731,2.804,2.879,2.954,3.029,3.105],32,8)';

I want to find the fitting Value of A with a a defined value of B and C with linear interpolation and "nearest", but i often get NaN

Michael Goebel 2022-9-7

编辑：Michael Goebel 2022-9-7

在 MATLAB Online 中打开

Edit: It works now as a . file with this code:

AA = [-20,-10,0,25,40,60,80,100]';  % Temperatur
BB = [0.5:0.5:16]; % Fluss
CC = reshape([0.142,0.234,0.325,0.417,0.508,0.599,0.69,0.781,0.872,0.963,1.054,1.145,1.235,1.326,1.417,1.508,1.598,1.689,1.779,1.87,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,0.173,0.265,0.356,0.447,0.539,0.63,0.72,0.811,0.902,0.993,1.083,1.174,1.265,1.355,1.445,1.536,1.626,1.716,1.806,1.896,1.987,2.08,2.173,2.265,2.358,2.451,2.543,2.636,2.731,2.827,2.924,3.021,0.301,0.393,0.483,0.574,0.664,0.753,0.843,0.932,1.022,1.114,1.206,1.299,1.395,1.491,1.587,1.683,1.781,1.879,1.977,2.076,2.176,2.275,2.375,2.474,2.573,2.673,2.773,2.873,2.973,3.072,3.172,3.271,0.318,0.608,0.694,0.78,0.865,0.951,1.038,1.129,1.221,1.314,1.408,1.503,1.597,1.692,1.788,1.883,1.978,2.072,2.167,2.262,2.357,2.451,2.545,2.638,2.732,2.826,2.919,3.011,3.104,3.196,3.288,3.379,0.313,0.612,0.898,1.172,1.339,1.393,1.452,1.515,1.58,1.646,1.712,1.78,1.848,1.916,1.985,2.054,2.123,2.193,2.263,2.334,2.406,2.477,2.55,2.623,2.696,2.77,2.844,2.918,2.992,3.067,3.142,3.217,0.31,0.599,0.871,1.129,1.376,1.513,1.554,1.6,1.649,1.7,1.753,1.807,1.863,1.92,1.978,2.038,2.1,2.163,2.227,2.292,2.359,2.426,2.495,2.564,2.634,2.704,2.776,2.848,2.92,2.993,3.067,3.142,0.3,0.564,0.808,1.043,1.278,1.516,1.631,1.658,1.689,1.723,1.761,1.803,1.849,1.899,1.952,2.007,2.064,2.124,2.186,2.249,2.314,2.38,2.448,2.517,2.587,2.658,2.73,2.803,2.877,2.951,3.026,3.102,0.29,0.538,0.773,1.011,1.254,1.501,1.67,1.689,1.713,1.742,1.777,1.817,1.861,1.908,1.959,2.013,2.069,2.128,2.188,2.251,2.316,2.382,2.45,2.519,2.588,2.659,2.731,2.804,2.879,2.954,3.029,3.105],32,8)';
AA1 = 25;
ZZ = interp2(AA,BB,CC',AA1,BB,'linear') %Suche A1 in A = Suche 
CC1 = 1.314;
BB1 = interp1(ZZ,BB,CC1,'linear')

But: When i try this code in Simulink as a matlab function, i get errors

Code of Simulink function:

function Q_Pumpe_von_Rotor = fcn(RotorRequest,Temp)
AA = [-20,-10,0,25,40,60,80,100]';  
BB = [0.5:0.5:16]; 
CC = reshape([0.142,0.234,0.325,0.417,0.508,0.599,0.69,0.781,0.872,0.963,1.054,1.145,1.235,1.326,1.417,1.508,1.598,1.689,1.779,1.87,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,1.96,0.173,0.265,0.356,0.447,0.539,0.63,0.72,0.811,0.902,0.993,1.083,1.174,1.265,1.355,1.445,1.536,1.626,1.716,1.806,1.896,1.987,2.08,2.173,2.265,2.358,2.451,2.543,2.636,2.731,2.827,2.924,3.021,0.301,0.393,0.483,0.574,0.664,0.753,0.843,0.932,1.022,1.114,1.206,1.299,1.395,1.491,1.587,1.683,1.781,1.879,1.977,2.076,2.176,2.275,2.375,2.474,2.573,2.673,2.773,2.873,2.973,3.072,3.172,3.271,0.318,0.608,0.694,0.78,0.865,0.951,1.038,1.129,1.221,1.314,1.408,1.503,1.597,1.692,1.788,1.883,1.978,2.072,2.167,2.262,2.357,2.451,2.545,2.638,2.732,2.826,2.919,3.011,3.104,3.196,3.288,3.379,0.313,0.612,0.898,1.172,1.339,1.393,1.452,1.515,1.58,1.646,1.712,1.78,1.848,1.916,1.985,2.054,2.123,2.193,2.263,2.334,2.406,2.477,2.55,2.623,2.696,2.77,2.844,2.918,2.992,3.067,3.142,3.217,0.31,0.599,0.871,1.129,1.376,1.513,1.554,1.6,1.649,1.7,1.753,1.807,1.863,1.92,1.978,2.038,2.1,2.163,2.227,2.292,2.359,2.426,2.495,2.564,2.634,2.704,2.776,2.848,2.92,2.993,3.067,3.142,0.3,0.564,0.808,1.043,1.278,1.516,1.631,1.658,1.689,1.723,1.761,1.803,1.849,1.899,1.952,2.007,2.064,2.124,2.186,2.249,2.314,2.38,2.448,2.517,2.587,2.658,2.73,2.803,2.877,2.951,3.026,3.102,0.29,0.538,0.773,1.011,1.254,1.501,1.67,1.689,1.713,1.742,1.777,1.817,1.861,1.908,1.959,2.013,2.069,2.128,2.188,2.251,2.316,2.382,2.45,2.519,2.588,2.659,2.731,2.804,2.879,2.954,3.029,3.105],32,8)';
%% AA1 = 25;
% ZZ = interp2(AA,BB,CC',AA1,BB,'linear'); %Suche A1 in A = Suche 
ZZ = interp2(AA,BB,CC',Temp,BB,'linear'); %Suche A1 in A = Suche
CC1 = 1.314;
% BB1 = interp1(ZZ,BB,CC1,'linear');
BB1 = interp1(ZZ,BB,RotorRequest,'linear');
Q_Pumpe_von_Rotor = BB1

Errors:

Simulink does not have enough information to determine output sizes for this block. If you think the errors below are inaccurate, try specifying types for the block inputs and/or sizes for the block outputs.

Component:MATLAB Function | Category:Coder error

The sizes of Xq and Yq must match. To interpolate on a grid, these inputs must be the outputs of MESHGRID.

Function 'MATLAB Function' (#35.1732.1767), line 8, column 6:

"interp2(AA,BB,CC',Temp,BB,'linear')"

Launch diagnostic report.

I am using Matlab 2017b

Srinivasan 2023-9-18

编辑：Srinivasan 2023-9-18

@Michael Goebel Thank you so much. Good find. Helped me a lot...

Michael Goebel 2023-10-4

My pleasure! I'm happy this helped

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Answer 2

Fangjun Jiang 2011-8-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12809-reverse-2d-lookup-table#answer_18182

To use non codegen supported functions, you need to declare eml.extrinsic('function_name'), but that is not what I am suggesting.

I recommend you creating a 2D lookup table data using the code above in MATLAB, making A and C as inputs, choosing 10 points for A and 9 points for C for example. You just need to do this once and then you can use a lookup table block in your Simulink model.

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Fangjun Jiang 2011-12-8

That is the code in the accepted answer. I've updated the answer to reflect a correction from the comments (due to the mix of row and column).

If that is not your use case, you may want to ask a separate question.

Guohong 2011-12-8

I think I got your idea. Just use lookup table dynamic to build another lookup table of Z and B, right?

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