I got an error as symbolic function expected 3 inputs and received 1 in the line no 5 (g1{r}(u)=​g1{r}(u)+(​u{i}-u1(i)​)./5*cheby​shevT(i-1,​2*x(r)-1))​. How can I fix that?

m=3;
u=sym('u',[1,m]);
g1 = cell(m+1, 1);
for r=1:m-1;
g1{r}(u) = sym(0);
for i = 1 : m+1
        g1{r}(u)=g1{r}(u)+(u{i}-u1(i))./(5)*chebyshevT(i-1,2*x(r)-1);
end
end

[Walter Roberson]

As I explained to you before, u is a vector of symbolic expressions. What are you expecting u{i} to be? u is not a cell array or table object or string object that {} indexing might be valid for.

[Surath Ghosh]

I want

u=[u1 u2 u3], where u1, u2, u3 are variables. Using u{i}, I want to access that variables like u{1}=u1, u{2}=u2, u{3}=u3.

What should I do now Sir?

[Walter Roberson]

MATLAB uses () for indexing not {}. Well, it uses {} too, but only for container objects such as cell arrays in which case the {} means to also remove the container after indexing.

[Walter Roberson]

you have u1(i) but u1 is scalar.

Also when you create

syms u [1 m]

the u1 u2 u3 that are created live only in the symbolic engine and you cannot name them at the MATLAB level.

syms u [1 m] 
syms(u)

will also create them at the MATLAB level.

[Surath Ghosh]

you suggested me earlier to write

syms u [1 m]
F = cell(m, 1);
for n = 1 : m
    F{n}(u) = appropriate body for f_n;
end

So, I tried to implement my code in that way, but it is not working. Actually my target is to write u=[u1 u2 u3], where u1,u2,u3 are variables. Using u{i}, I got u{1}=u1, u{2}=u2, u{3}=u3.

So, I can access the variables.

Now I have changed u1 as v. still now I am getting same error msg as symbolic function expected 3 inputs and receive 1. Here using {}, I want to access g1_1(u), g1_2(u).....

where g1 = cell(m+1, 1), expecting g1 is a cell array.

why am I getting that error msg? Can I write the code in this way or not?

Please explain the error message.

m=3;
u=sym('u',[1,m]);
g1 = cell(m+1, 1);
for r=1:m-1;
g1{r}(u) = sym(0);
for i = 1 : m+1
        g1{r}(u)=g1{r}(u)+(u{i}-v(i))./(5)*chebyshevT(i-1,2*x(r)-1);
end
end

[Walter Roberson]

g1{r}(u) = sym(0);

That syntax is the same as

g1{r} = symfun(sym(0), u)

which builds a symbolic function which accepts three distinct inputs and returns a value.

g1{r}(u)=g1{r}(u)+(u{i}-v(i))./(5)*chebyshevT(i-1,2*x(r)-1)

That code attempts to call g1{r} with a single input that is a vector of length 3.

To call g1{r} you need to pass in the elements of u as distinct inputs.

Using u{i}, I got u{1}=u1, u{2}=u2, u{3}=u3.

Which MATLAB release are you using? It would take me a bit of time to get a working copy of the old Maple-based MATLAB to test to be absolutely sure, but I guarantee that in any MuPAD based release of the symbolic toolbox, that what you indicate is incorrect.

m=3;
u=sym('u',[1,m]);
i = 1;
u{i}

Brace indexing is not supported for variables of this type.

Error in sym/subsref (line 907)

R_tilde = builtin('subsref',L_tilde,Idx);

{} is not valid for vectors of symbolic expressions.

It is not productive for me to keep arguing with you. Here is the code. Notice the complete lack of {} indexing for the symbolic vector.

m = 3;

x = rand(1,m-1);  %replace with your actual data, which must be at least m-1 long
v = rand(1,m+1);  %replace with your actual data, which must be at least m+1 long

u = sym('u',[1,m+1]);
uc = num2cell(u);
g1 = cell(m-1, 1);
for r=1:m-1
    g1{r}(u) = sym(0);
    for i = 1 : m+1
        g1{r}(u)=g1{r}(uc{:})+(u(i)-v(i))./(5)*chebyshevT(i-1,2*x(r)-1);
    end
end

I had to change the size of some of the arrays to fit your code. I took your "r=1:m-1" and "i=1:m+1" to be definite truths and repaired everything around those lines. That requires that u become a vector of length m+1 instead of length m, because you index u at i and i goes to m+1 . I had to assume that something was right about your code...

Answer 1

[Walter Roberson]

m = 3;

x = rand(1,m-1);  %replace with your actual data, which must be at least m-1 long
v = rand(1,m+1);  %replace with your actual data, which must be at least m+1 long

u = sym('u',[1,m+1]);
uc = num2cell(u);
g1 = cell(m-1, 1);
for r=1:m-1
    g1{r}(u) = sym(0);
    for i = 1 : m+1
        g1{r}(u)=g1{r}(uc{:})+(u(i)-v(i))./(5)*chebyshevT(i-1,2*x(r)-1);
    end
end

Under the assumption that the two "for" lines were coded correctly by the user; everything else was modified to fit that.

[Surath Ghosh]

Okay sir. Thank you.

Answer 2

[Surath Ghosh]

Thank you so much sir for your kind reply.

I am using R2016a.

[Walter Roberson]

I guarantee that in that release you cannot use {} indexing of symbolic vectors.