Simscape tablelookup input value

I'm trying to create a custom simscape component and I'm facing problem using "tablelookup".

the component has n spatial section. A physical parameter "y" of each section should be determined using "tablelookup" based on user defined values in the parameter section.

a very simplified code to reproduce the case is as follow:

component Vect
 outputs
   f = 0;
 end
 parameters 
    u1 = [1 1 ];
    u2 = [1 1.5 ];
 end
 parameters(Access=private)
    x1d = [1 2 3 4];
    x2d = [1 2 3];
    y = [1 2 3; 3 4 5; 5 6 7; 7 8 9];
    
 end
 equations
    f == tablelookup(x1d, x2d, y, u1, u2, interpolation = linear, extrapolation = nearest);
 end
end

I'm getting the following error while compiling:

Error compiling Simscape network for model sim_Vect.
Caused by:
['sim_Vect/Simscape Component']: Function, tablelookup, is wrong.  Please check 1) 
    whether input data points have correct sizes; 2) query values are scalar; 3) 
    query values and table data have the commensurate units; and 4) constants or 
    compile time parameters are passed to interpolation and extrapolation argument.  In Vect (line 19)
Argument 1 = [1 2 3 4] 
Argument 2 = [1 2 3] 
Argument 3 = [4x3 double] 
Argument 4 = [1 1] 
Argument 5 = [1 1.5000] 
x1d = [1 2 3 4] 
x2d = [1 2 3] 
y = [4x3 double] 
u1 = [1 1] 
u2 = [1 1.5000] 
Component:Simulink | Category:Model error

My problem is that it seems to me like tablelookup can only work with single input value.

The point is that the number of sections n is probably unknown and even if's known it could be very big(100 to 1000 entry) so I can't call tablelookup for every single section separatly.

As I'm not very experienced with simscape, I might be missing something or misunderstanding the tablelook up function.

So could you please help me to realise this functionality or share a workarround?

Answer 1

[J Chen]

Several options: 1) use the Simscape built-in PS Lookup Table (2D) block instead of a custom block. 2) study the example here. 3) build the component with Simulink blocks and use PS-Simulink converters to interface with your Simscape model.

[Mahmoud Seboui]

Hi J Chen,

Thank you for your response!

Actually this is not the whole code but part of it, so my final goal is not creating a lookup table but to use it within my component.

I already have the simulink model (of the component) and I use it in the way you mention in (3) but I wanted to create the component in simscape with the hope to increase the performace of the whole model.

[J Chen]

I think the problem might be that the u1 and u2 in the following command need to be scaler. They can't be vectors as in your code.

f == tablelookup(x1d, x2d, y, u1, u2, interpolation = linear, extrapolation = nearest);

The error message (2) seems to support my assumption.

Answer 2

[Shubham Kashyap]

In the ‘tablelookup’ documentation, it specifies:

“For two-dimensional table lookup, yd must be a matrix, with the size matching the dimensions defined by the input data sets. For example, if x1d is a 1-by-m array, and x2d is a 1-by-n array, then yd must be an m-by-n matrix.”

tablelookup(x1d, x2d, yd, x1, x2, interpolation = linear|cubic|spline, extrapolation = linear|nearest)

This means that m x n matrix is referenced by:

A) First input lookup data (x1d) references rows (m) of a lookup table.

B) and the second input lookup data (x2d) references the column (n) of a lookup table.

For example, the proper input order using 'tablelookup' function is shown below:

density_out = tablelookup(B.temperature, B.pressure, B.density, T_out, P_out, interpolation = spline, extrapolation = nearest);

For the code above, since m x n is ‘pressure’ x ‘temperature’:

A) x1d – should have input lookup data of pressure data

B) x2d – should have input lookup data of temperature data.

Corrective Methods:

A) Enter the input lookup data set as per order mentioned above.

B) OR transpose the lookup table.

Please refer to following documentation on ‘tablelookup’ for more information on interpolation method:

http://www.mathworks.com/help/physmod/simscape/lang/tablelookup.html