MATLAB Incorrect number or types of inputs or outputs for function solve.

Hi, I am trying to solve for p here This code gives error Incorrect number or types of inputs or outputs for function solve.

Error in stats1 (line 16) solutions = solve(sf == 0, p);

if true
  % clc
syms p 
n = input('Enter how many times to repeat vars in combinations(): ');
R = repmat({[p, p-1]}, 1, n);  
T = combinations(R{:});
disp(['Combinations of vars repeated ', num2str(n), ' times:']);
disp(T);
pm = log(prod(T, 2));
ps = prod(T, 2);
k = ps .*pm ;
disp('Product of each combination:');
disp(k)
sm = sum(k);
disp(sm)
sf = diff(sm, p)
solutions = solve(sf == 0, p);
end

Answer 1

[Steven Lord]

Let's choose a small value for n (since the input command cannot run on MATLAB Answers) and see what you're trying to pass into the solve function.

n = 3;
syms p 
R = repmat({[p, p-1]}, 1, n);  
T = combinations(R{:});
disp(['Combinations of vars repeated ', num2str(n), ' times:']);

Combinations of vars repeated 3 times:

disp(T);

    Var1     Var2     Var3 
    _____    _____    _____

    p        p        p    
    p        p        p - 1
    p        p - 1    p    
    p        p - 1    p - 1
    p - 1    p        p    
    p - 1    p        p - 1
    p - 1    p - 1    p    
    p - 1    p - 1    p - 1

pm = log(prod(T, 2));
ps = prod(T, 2);
k = ps .*pm ;
disp('Product of each combination:');

Product of each combination:

disp(k)

                prod            
    ____________________________

    p^3*log(p^3)                
    p^2*log(p^2*(p - 1))*(p - 1)
    p^2*log(p^2*(p - 1))*(p - 1)
    p*log(p*(p - 1)^2)*(p - 1)^2
    p^2*log(p^2*(p - 1))*(p - 1)
    p*log(p*(p - 1)^2)*(p - 1)^2
    p*log(p*(p - 1)^2)*(p - 1)^2
    log((p - 1)^3)*(p - 1)^3    

sm = sum(k);
disp(sm)

                           prod                       
    __________________________________________________

    log((p - 1)^3)*(p - 1)^3 + p^3*log(p^3) + 3*p*l...

sf = diff(sm, p)

sf = table
                           prod                       
    __________________________________________________

    3*log((p - 1)^3)*(p - 1)^2 + 6*(p - 1)^2 + 3*p^...

The solve function is not designed to accept a table as the first input. But if you extract the value from the table and use that in your solve call:

sol = solve(sf.prod == 0, p)

Warning: Unable to solve symbolically. Returning a numeric solution using vpasolve.

sol = 

Or if you extracted the matrix of symbolic variables from the table before you started operating on it:

T2 = T.Variables

T2 = 

pm = log(prod(T2, 2));
ps = prod(T2, 2);
k = ps .*pm ;
sm = sum(k);
sf2 = diff(sm, p);
sol2 = solve(sf2 == 0, p)

Warning: Unable to solve symbolically. Returning a numeric solution using vpasolve.

sol2 = 

isequal(sf2, sf.prod)

ans = logical
   1