Undefined operator '-' for input arguments of type 'cell' in code that worked ~2 years ago

I'm trying to revive an optimization utility that I coded up a couple of years ago. The complete code relies on reading in some data files so I can't post a complete minimal working (or non-working) example, but I'll try to be as thorough as I can in hopes this is an easy fix. I'm not a frequent MatLab user, so I imagine things may have changed since I wrote this....

The very short version is that I get the subject error on this line of code

c(i)= ((1-G) .* X(:,i)) - X(:,i+1);

This is in a function that handles the constraints for an optimization problem. X is passed in, and represents a candidate solution, so I don't understand how it's of type cell.

Here's a longer walk through the code

%we used file dialog boxes to get the location of the input file
[num, txt, raw] = xlsread(openFile,xlSheet,xlRange);

%start gathering up the problem parameters

%requirements matrix
R = num(1:numActivities,3:7);

%weights matrix
W = num(1:numActivities,2);

%available funding
maxFunds = num(1,19:23);

%intial solution - all zeros
x0 = zeros(numActivities,5);

%lower bounds is the same
lb = x0;

%upper bounds is the requirements
ub = R;

%need to ask for a turbulence factor
G = inputdlg('Please enter the turbulence factor.  This is a number between 0 and 1.','Turbulence Factor',1,{'0.15'});

%I told you this was old code...

%at work version 2014b, and then the options are   
%MaxFunEvals, MaxIter  

%at home version 2017a, and the options are
%MaxFunctionEvaluations, MaxIterations

if verLessThan('matlab','9.2.0')
    options = optimoptions(@fmincon,'Algorithm','sqp','MaxFunEvals',100000,'MaxIter',100000);
else
    options = optimoptions(@fmincon,'Algorithm','sqp','MaxFunctionEvaluations',100000,'MaxIterations',100000);
end
p = gcp('nocreate');   % if no pool, don't create a new one 
if isempty(p)
    parpool;
end

ms=MultiStart('UseParallel',true);

%In reality there are several different ways of handling the constraints
%and the objective function.  I use dialogs to get the selections from the
%user and there would be an if statement here to use the right
%@function_names
%For simplicity I'm just including this one...it throws the error

problem = createOptimProblem('fmincon','objective',@base_objective,'nonlcon',@turbulence_constraints,'x0',x0,'lb',lb,'ub',ub,'options',options);
        
[x, fval] = run(ms,problem,100)


% we have to go ahead and declare all of the functions 
% and then use the ones we want

% base constraints
    function [ c, ceq ] = base_constraints(X)
        %base_constraints multi-year constraints function
        %   no turbulence
        %   matrix X is the decision variables (funding levels)
        %   matrix R is the requirements

        % ub and lb take care of our upper and lower bounds for X
        % so all we really need to ensure is that the totals
        % don't exceed each year's funding

        S=sum(X);
        c=[];
        ceq = [S(1) - maxFunds(1);
               S(2) - maxFunds(2);
               S(3) - maxFunds(3);
               S(4) - maxFunds(4);
               S(5) - maxFunds(5)];
    end


% turbulence constraints
    function [ c, ceq ] = turbulence_constraints(X)
        %   G is the turbulence factor
        %   year N can't be a decrease of more than G% from year N-1
        %   matrix X is the decision variables (funding levels)
        %   matrix R is the requirements
        
        % ub and lb take care of our upper and lower bounds for X
        % so all we really need to ensure is that the totals
        % don't exceed each year's funding
        % and that the turbulence requirement is met

        S=sum(X);
        
        c=zeros(4,1);
        for i = 1:4
            c(i)= ((1-G) .* X(:,i)) - X(:,i+1);
        end
        
        ceq = [S(1) - maxFunds(1);
               S(2) - maxFunds(2);
               S(3) - maxFunds(3);
               S(4) - maxFunds(4);
               S(5) - maxFunds(5)];
    end

I hope that's enough info to be useful in figuring this out...any help is most appreciated!

Answer 1

[Walter Roberson]

G = inputdlg('Please enter the turbulence factor.  This is a number between 0 and 1.','Turbulence Factor',1,{'0.15'});

inputdlg() always returns a cell array, never a numeric value. It has never returned a numeric value.

            c(i)= ((1-G) .* X(:,i)) - X(:,i+1);

with your spacing, that just might be inside a nested function and so G might be a shared variable here. But G is a cell array, not a number.