Conditionals in argument blocks

Is it possible to make the default value of one optional variable depend on the value of another optional variable?

In particular suppose I define a function with required argument shape and optional argument v1 so that when. The variable shape can take one of two names, and the variable v1 has different default values depending on the value of shape, or else can be specificed by a name value pair.

I should be able to make the calls

myFunction('rectangle')

and the arguments block should assign v1=[1 0].

If I make the call

myFunction('triangle')

and the arguments block should assign v1=[1 sqrt(3)]/2

But then I should be able to override the defaults with the calls

myfunction('rectangle',v1=[6 4])

or else

myfunction('rectangle',v1=[5 21])

and opts.v1 will take the value specified

Answer 1

[Lawrence]

This is possible because expressions are allowed as the default value, and you can use prior arguments in expressions for later arguments.

function v1 = myFunction(shape,v1)
arguments
    shape {mustBeMember(shape,{'rectangle','triangle'})}
    v1 (1,2) double = calculateDefaultV1(shape)
end
end

function v1 = calculateDefaultV1(shape)
switch shape
    case 'rectangle'
        v1 = [1 0];
    case 'triangle'
        v1 = [1 sqrt(3)]/2;
end
end

Note, however, that since Name/Value pairs can be supplied by the caller in any order or omitted entirely, you're not allowed to use the value of a name-value argument in an arguments block default value expression. So, this is illegal:

function v1 = bugged_myFunction(opts)
arguments
    opts.shape {mustBeMember(opts.shape,{'rectangle','triangle'})}
    opts.v1 (1,2) double = calculateDefaultV1(opts.shape) %% Cannot use opts.shape here
end
end

function v1 = calculateDefaultV1(shape)
switch shape
    case 'rectangle'
        v1 = [1 0];
    case 'triangle'
        v1 = [1 sqrt(3)]/2;
end
end

You'd need to either make shape a positional argument or hand-roll your default value like Chidvi Modala described in their answer, but using ~isfield(opts,'v1') instead of nargin or exist('v1','var').

Answer 2

[Chidvi Modala]

You may refer to the following piece of code

function v1 =  myfunction(shape, varargin)
if strcmp(shape,'rectangle')
    if nargin >1
        v1 = varargin{1};
    else
        v1=[1 0];
    end
elseif strcmp(shape,'triangle')
    if nargin >1
        v1 = varargin{1};
    else
        v1=[1 sqrt(3)]/2;
    end
end
end

[Roy Goodman]

Thanks, but I'm actually trying to do something a lot more complicated than this but simplified the essence to write the question. I want to use name/value pairs, not varargin, and thus use an argument block, as stated in the question.

[Chidvi Modala]

The following link might be of help to you

https://www.mathworks.com/help/matlab/matlab_prog/function-argument-validation-1.html

[Roy Goodman]

Thanks for your response. I read the documentation first and then saw no way to acccomplish what I'm trying to do. That's why I posted a question.