I cant get this matlab function to work.

I have to use fsolve() to call this function.

I want to input a guess for fsolve() and I want two answers for each of the equations for Rblas4(1) and Rblas4(2).

my error reads:

error: 'T' undefined near line 19 column 18

error: called from

arco at line 19 column 14

My script it:

function Rblas4=arco(T)
    p=51;
    v=35;
    n=50;
    r=.08206;
    spv=v/n;
    Tca=150.87;
    wa=1.002;
    Tcc=304.2;
    Pcc=72.9;
    Pca=48.3;
    wc=.225;
    aa=.42747*((r*Tca)^2/Pca);
    ac=.42747*((r*Tcc)^2/Pcc);
    ba=.08664*((r*Tca)/Pca);
    bc=.08664*((r*Tcc)/Pcc);
    ma=.48508+1.55171*wa-.1561*(wa-1)^2;
    mc=.48508+1.55171*wc-.1561*wc^2;
    RBlas4(1)=(r*T(1))/(spv-ba)-aa*(1+ma*(1-sqrt(T(1)/Tca)))^2/(spv*(spv-ba))-p;
    RBlas4(2)=(r*T(2))/(spv-bc)-ac*(1+mc*(1-sqrt(T(2)/Tcc)))^2/(spv*(spv-bc))-p;
    end 
   

THANK YOU

Answer 1

[madhan ravi]

EDITED

You should call the function properly with input T like shown below:

T=[3 8] %example
Rblas4=arco(T)           %function call

function RBlas4=arco(T)  %function definition
    p=51;
    v=35;
    n=50;
    r=.08206;
    spv=v/n;
    Tca=150.87;
    wa=1.002;
    Tcc=304.2;
    Pcc=72.9;
    Pca=48.3;
    wc=.225;
    aa=.42747*((r*Tca)^2/Pca);
    ac=.42747*((r*Tcc)^2/Pcc);
    ba=.08664*((r*Tca)/Pca);
    bc=.08664*((r*Tcc)/Pcc);
    ma=.48508+1.55171*wa-.1561*(wa-1)^2;
    mc=.48508+1.55171*wc-.1561*wc^2;
    RBlas4=[(r*T(1))/(spv-ba)-aa*(1+ma*(1-sqrt(T(1)/Tca)))^2/(spv*(spv-ba))-p;  %change this line too
           (r*T(2))/(spv-bc)-ac*(1+mc*(1-sqrt(T(2)/Tcc)))^2/(spv*(spv-bc))-p];
end

Note: matlab is case sensitive Rblas4 should be RBlas4

[madhan ravi]

see edited answer it works

[Rodrigo Blas]

Well, I got it to out put something. thank you

sorry but maybe i didnt ord my quesiton right.

but I'm trying to make it so that fsolve() solves for T(1) and T(2). They are both unknown variables. The two equations that are in the Rblas4 matrix are equal to zero

[madhan ravi]

please upload the full code I'm having difficulty in understanding your question

[Rodrigo Blas]

This is in the editor:

function Rblas4=arco(T)
    p=51;
    v=35;
    n=50;
    r=.08206;
    spv=v/n;
    Tca=150.87;
    wa=1.002;
    Tcc=304.2;
    Pcc=72.9;
    Pca=48.3;
    wc=.225;
    aa=.42747*((r*Tca)^2/Pca);
    ac=.42747*((r*Tcc)^2/Pcc);
    ba=.08664*((r*Tca)/Pca);
    bc=.08664*((r*Tcc)/Pcc);
    ma=.48508+1.55171*wa-.1561*(wa-1)^2;
    mc=.48508+1.55171*wc-.1561*wc^2;
    Rblas4=[(r*T(1))/(spv-ba)-aa*(1+ma*(1-sqrt(T(1)/Tca)))^2/(spv*(spv-ba))-p;
    (r*T(2))/(spv-bc)-ac*(1+mc*(1-sqrt(T(2)/Tcc)))^2/(spv*(spv-bc))-p];
    end 
In the command window:
guess=[10 10]
guess =
   10   10
>> fsolve('arco',guess)
error: invalid call to script C:\Users\rodri\arco.m
error: called from
    fsolve at line 204 column 8

This is the full code with your adjustments. I want it to return the actual value of T for both equations in Rblas4 matrix. Both equations are equal to zero are both equal to zero and T(1) and T(2) are unknown

This is an example of what i want it to do:

This example shows how to solve two nonlinear equations in two variables. The equations are

Convert the equations to the form .

Write a function that computes the left-hand side of these two equations.

function F = root2d(x)
F(1) = exp(-exp(-(x(1)+x(2)))) - x(2)*(1+x(1)^2);
F(2) = x(1)*cos(x(2)) + x(2)*sin(x(1)) - 0.5;

Save this code as a file named root2d.m on your MATLAB® path.

Solve the system of equations starting at the point [0,0].

fun = @root2d;
x0 = [0,0];
x = fsolve(fun,x0)
Equation solved.

[madhan ravi]

change this

fsolve('arco',guess) % no strings to call the function ' ' should be @ -> function handle 

to this

fsolve(@arco,guess)  

[Rodrigo Blas]

new error:

fsolve(@arco,guess)

error: 'k' undefined near line 5 column 21

error: called from

norm at line 5 column 6

fsolve at line 207 column 6

>>

[madhan ravi]

wierd this is the answer I got

>> COMMUNITY

Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the default value of the function tolerance, and
the problem appears regular as measured by the gradient.

<stopping criteria details>

ans =
  424.7032  458.5318
>> 

[Rodrigo Blas]

got it! THANK YOU SO MUCH!

What happened is I didnt click run.

You were very helpful :)

[madhan ravi]

Anytime :)