Error in optimconstr() when used with single string vs array of string

I'm working on MATLAB Version: 9.12.0.1884302 (R2022a) with Optimization Toolbox (9.3).

I have created 2 sets flight_name_set & Edges of type string

optimconstr gives the below error whenever the set is of single value but not on multiple values.

Error using optimconstr

Dimensions specifications must be a positive integer, string array, or a

cell array of character vectors.

For e.g

When Edges has 2 values Then there is no error.

flight_name_set = 

  1×5 string array

    "Small-tt-1"    "Medium-yy-2"    "Medium-rr-3"    "Jumbo-mm-4"    "Jumbo-zz-5"

Edges = 

1×2 string array

"W-Y"    "S-Y"
optimconstr(Edges, flight_name_set, flight_name_set)

ans = 

  2×5×5 OptimizationConstraint array with properties:

    IndexNames: {{1×2 cell}  {1×5 cell}  {1×5 cell}}
     Variables: [1×1 struct] containing 0 OptimizationVariables

  See constraint formulation with show.

but when Edges have 1 value there is error

flight_name_set = 

  1×5 string array

    "Small-tt-1"    "Medium-yy-2"    "Medium-rr-3"    "Jumbo-mm-4"    "Jumbo-zz-5"
  
Edges = 

    "W-Y"
optimconstr(Edges, flight_name_set, flight_name_set)
Error using optimconstr
Dimensions specifications must be a positive integer, string array, or a cell array of character vectors.

With hit and trial I have to put a check on length and then use {Edges{:}} if there is only 1 value. Is there a way to use genralise statements?

Answer 1

[Raghunathraju]

Hi Raviraj,

The 'optimconstr' function cannot have a single argument as string, The input arguments can be a string array, a cell array, or it can be a positive integer .If you want to use a string as an input argument then it must be an array of strings.

[Ravi Raj Saxena]

But what if I have only 1 element?

[Aurele Turnes]

When you have a single element, you should use a cell array of character vectors like this:

optimconstr(cellstr(Edges), flight_name_set, flight_name_set)

This is because optimconstr and optimexpr go hand-in-hand with optimvar, which accepts string inputs and name-value arguments. For this reason, when writing:

optimvar("x", "Typo", "integer")

It is impossible to know if this is a typo and means:

optimvar("x", "Type", "integer")

or if this means:

optimvar("x", {'Typo'}, {'integer'})

To avoid silently returning the wrong answer, we error and require to pass a cell array for a single string input. Optimexpr and optimconstr behave similarly for consistency.