what particular need of this , why we need it to be in a 'sol' what is the benefit for this

global z P
clear sol
z=[0.2 0.8];
P=5*14.69;
options = optimset('Display','off');
[X]=fsolve(@PT3,[0.01 0.9 0.01 0.9 500],options);
x0=X;
sol(1,1)=P;
sol(2,1)=X(5);
for i=1:63
    P=(5+i)*14.69;
    [X]=fsolve(@PT3,x0,options);
    x0=X;
    sol(1,i+1)=P;
    sol(2,i+1)=X(5);
end
sol(1,64)=968;
sol(2,64)=513+459.67;
plot(((sol(2,:)-459.67)-32)./1.8+273.15,sol(1,:)./14.69,'b')
hold on
clear sol
z=[0.2 0.8];
P=5*14.69;
options = optimset('Display','off');
[X]=fsolve(@PT4,[0.01 0.9 0.2 0.8 700],options);
x0=X;
sol(1,1)=P;
sol(2,1)=X(5);
for i=1:59
    P=(5+i)*14.69;
    [X]=fsolve(@PT4,x0,options);
    x0=X;
    sol(1,i+1)=P;
    sol(2,i+1)=X(5);
end
sol(1,61)=968;
sol(2,61)=513+459.67;
plot(((sol(2,:)-459.67)-32)./1.8+273.15,sol(1,:)./14.69,'r')
clear sol
z=[0.7 0.3];
P=5*14.69;
options = optimset('Display','off');
[X]=fsolve(@PT3,[0.7 0.3 0.999 0.001 350],options);
x0=X;
sol(1,1)=P;
sol(2,1)=X(5);
for i=1:99
    P=(5+i)*14.69;
    [X]=fsolve(@PT3,x0,options);
    x0=X;
    sol(1,i+1)=P;
    sol(2,i+1)=X(5);
end    
sol(1,101)=1550;
sol(2,101)=770;
plot(((sol(2,:)-459.67)-32)./1.8+273.15,sol(1,:)./14.69,'m')
clear sol
z=[0.7 0.3];
P=5*14.69;
options = optimset('Display','off');
[X]=fsolve(@PT4,[0.01 0.9 0.3 0.7 600],options);
x0=X;
sol(1,1)=P;
sol(2,1)=X(5);
for i=1:99
    P=(5+i)*14.69;
    [X]=fsolve(@PT4,x0,options);
    x0=X;
    sol(1,i+1)=P;
    sol(2,i+1)=X(5);
end    
sol(1,101)=1550;
sol(2,101)=770;
plot(((sol(2,:)-459.67)-32)./1.8+273.15,sol(1,:)./14.69,'g')

Answer 1

[David Young]

"sol" is the name of a variable. You could replace "sol" by any other name, and as long as you are consistent (you change every "sol" to the same thing) your code will work exactly the same. So there's nothing special about a "sol" - it's just a name.

In the code, the value of the variable "sol" is an array. This is a data structure with multiple elements, so you can hold many different numerical values in one place, and access individual elements by row and column, as in sol(1,101).