Interpolate, find - excel lookup equivalent

I completed an excercise many years ago using Excel for a university task.

I recently started using Matlab and would like to repeat the task, but I am stuck and Im not sure what function to use.

I have a variable t, but now I need to find what range t lies within to extract a corresponding value. In excel the function I used was lookup, where it would look for the value in the table.

With Matlab, im not sure if it is interpolate, or find. I tried with interpolate and couldnt get it to work using this below, it could be that I have used this incorrectly or due to the format of the table. Any ideas??

c = interp1(Flange(1:4,1:2), Flange(1:4,3), t);

Many thanks!

Answer 1

[Star Strider]

The table appears to work stepwise. The interp1 function can interpolate using several options, here 'previous', 'nearest', and 'next' could apply. Choose the method that does what you want.

Example —

S235 = [16      235
        40      225
        63      215
        80      215];
    
fy_fcn = @(Thickness) interp1(S235(:,1), S235(:,2), Thickness, 'nearest');

Thickness = 25;
fy = fy_fcn(Thickness)

producing:

fy =
   235

.

[Omar Aziz]

that is great, thank you for the answer!

what does the @(Thickness) do exactly?

[Star Strider]

As always, my pleasure!

I created ‘fy_fcn’ as an anonymous function. It works just as any other function, and can be incorporated into a script (as I did here) without it having to be defined at the end of the script or saved as a separate function file. Anonymous functions are extremely useful in a variety of situations. They are explained in Anonymous Functions. The ‘@’ operator defines a function handle. See What Is a Function Handle? for more information on them.

[Omar Aziz]

Thanks for the explanation!

I have a follow up question.

Prior to this, I ask for a prompt so the user can specifiy the steel grade.

I am having trouble combing the two parts of the script - any ideas?

It seems if I offer non numeric choices ('S235' etc) then substituting S235 (from the answer above) for steel_grade I got an error.

steel_grade = questdlg('What is the steel grade (S)', mfilename, 235, 275, 355,'quit');

[Star Strider]

As always, my pleasure!

I would do something like this:

S235 = [16      235
        40      225
        63      215
        80      215];
    
S275 = [16      275
        40      265
        63      255
        80      245];

S355 = [16      355
        40      345
        63      335
        80      325];

steel_grade = questdlg('What is the steel grade (S)', mfilename, 235, 275, 355,'quit');
thicknsc = inputdlg('Thickness:', 'What is the thickness?');
thickns = sscanf(thicknsc{:},'%f');

switch steel_grade
    case 235
        fy = interp1(S235(:,1), S235(:,2), thickns, 'nearest')
    case 275
        fy = interp1(S275(:,1), S275(:,2), thickns, 'nearest')
    case 355
        fy = interp1(S355(:,1), S355(:,2), thickns, 'nearest')
end

I tested it, and it works for all of them. Tha anonymous function is not necessary here, since in this context it simply adds another layer of complexity.