Convert a three 10x2 matrix into a 2D lookup table data

I have a three 10x2 data in terms of a,b,c and i want to convert these data into 2D lookup table ie row should be a ,column should be b and the value to be lookup should be c,i tried doing interp2(x,y,z,xq,yq) but am getting an error of

Error using griddedInterpolant

Grid arrays must have NDGRID structure.

Can someone please help how to solve this issue

[Matt J]

Not without a .mat file attachment with a,b,c.

[Sandeep Nair]

a=[

0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.16 0.16 0.16 0.16 0.16 0.15 0.15

0.33 0.32 0.32 0.31 0.31 0.31 0.30

0.49 0.48 0.48 0.47 0.47 0.46 0.45

0.65 0.64 0.64 0.63 0.62 0.61 0.60

0.82 0.81 0.80 0.79 0.78 0.76 0.75 ]

b=[

0.46 0.47 0.49 0.51 0.53 0.54 0.56

0.88 0.91 0.94 0.97 1.01 1.04 1.07

2.13 2.21 2.29 2.37 2.44 2.52 2.60

4.22 4.37 4.53 4.69 4.84 5.00 5.16

7.14 7.41 7.67 7.94 8.20 8.47 8.73

10.90 11.31 11.71 12.12 12.52 12.92 13.33 ]

c=[

0.14 0.15 0.15 0.15 0.15 0.15 0.16

0.15 0.15 0.15 0.15 0.16 0.16 0.16

0.15 0.15 0.16 0.16 0.16 0.16 0.16

0.15 0.16 0.16 0.16 0.16 0.17 0.17

0.16 0.16 0.16 0.17 0.17 0.17 0.17

0.16 0.16 0.17 0.17 0.17 0.17 0.18 ]

[Sandeep Nair]

Lets say this is the matrix

[Dyuman Joshi]

You can do it with logical indexing as well.

a=[0.00  0.00  0.00  0.00  0.00  0.00  0.00; 
  0.16  0.16  0.16  0.16  0.16  0.15  0.15;
  0.33  0.32  0.32  0.31  0.31  0.31  0.30; 
  0.49  0.48  0.48  0.47  0.47  0.46  0.45; 
  0.65  0.64  0.64  0.63  0.62  0.61  0.60; 
  0.82  0.81  0.80  0.79  0.78  0.76  0.75];
b=[0.46  0.47  0.49  0.51  0.53  0.54  0.56; 
  0.88  0.91  0.94  0.97  1.01  1.04  1.07; 
  2.13  2.21  2.29  2.37  2.44  2.52  2.60; 
  4.22  4.37  4.53  4.69  4.84  5.00  5.16; 
  7.14  7.41  7.67  7.94  8.20  8.47  8.73; 
  10.90  11.31  11.71  12.12  12.52  12.92  13.33];
c=[0.14  0.15  0.15  0.15  0.15  0.15  0.16;
  0.15  0.15  0.15  0.15  0.16  0.16  0.16; 
  0.15  0.15  0.16  0.16  0.16  0.16  0.16; 
  0.15  0.16  0.16  0.16  0.16  0.17  0.17; 
  0.16  0.16  0.16  0.17  0.17  0.17  0.17; 
  0.16  0.16  0.17  0.17  0.17  0.17  0.18];
[m,n]=size(c);
x=randi(m)

x = 6

y=randi(n)

y = 1

c(abs(a-a(x,y))<1e-2&abs(b-b(x,y))<1e-2)

ans = 0.1600

c(x,y)

ans = 0.1600

[Sandeep Nair]

i want to input a random number which is should be inbetween the numbers in a and b and get the value from c, here instead of a random number indices are used to get the number

[Dyuman Joshi]

What exactly would be a random number inbetween the numbers in a and b then?

[Sandeep Nair]

Random number would be like a=0.55 and b = 6.3 ,basically it should look for value if its not there then it should interpolate and give the answer in c

[Dyuman Joshi]

Alright. In that sense, what if the value is a=0, b=0.5. Which value of c should be interpolated?

Similarly for a=0, b=0.52, c=?

[Sandeep Nair]

Here the condition which arise is a=0.45 and b=1.5 ,the condition which you are saying will not arise i want to interpolate between the points of the matrix

Answer 1

[Aditya Srikar]

To create a 2D lookup table where the rows are values of `a`, the columns are values of `b`, and the entries are values of `c`, you can use MATLAB's `interp2` function. Here are the steps to do this:

1. Create a grid of `a` and `b` values using the `meshgrid` function in MATLAB:

[a_grid, b_grid] = meshgrid(a_values, b_values);

2. Use the `interp2` function to interpolate the values of `c` on this grid:

interp_c = interp2(a, b, c, a_grid, b_grid, 'spline');

Here, `inter_c` is the interpolated value of `c` on the grid, and the `'spline'` option specifies cubic spline interpolation.

Make sure that the dimensions of `a`, `b`, and `c` are the same and that there are no NaN or Inf values in `a`, `b`, or `c`.