MATLAB: Solving a formula in Matlab

formula

Hello everyone,

In the following formula : X= 2y + 10 log(1+ E/S)

I want the user to input X, y, and S. Is there anyway i can get matlab to give me the value of E without having to rewrite the formula?

Thank you so much!

Best Answer

x = input('Enter the value of x: '); % request user input
y = input('Enter the value of y: ');
S = input('Enter the value of S: ');
f = @(E) 2.*y + 10*log(1+ E./S) - x; % create an anonymous function
[Eval, fval]= fsolve(f, 1); % solve your equation

or you can also:

syms E
f = 2.*y + 10*log(1+ E./S) == x;
solve(f, E)

If log refers to the base of 10 rewrite f by replacing log with log10.

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MATLAB: My code says too many output arguments

Give your functions outputs:

newton
function newton
x0 = input('Enter the initial guess value, x: ');
tolerance = input('Enter the tolerance value, tol: ');
max_i = input('Enter the maximum no. of iteration, max_i: ');
r = input('Enter the value of relative roughness, e/D: ');
RN = input('Enter the Reynolds number, RN: ');
f = input('Enter the Friction factor, f: ');
c = colebrook/colebrook_deriv;
x=x0;
for i=1:max_i
    y = x;
    x = y - (c);
    if abs(x-y)<= tolerance
        disp(['root = ', num2str(x)])
        break
    end
end
fprintf('The number of iterations: %d\n', i)
    function CFd = colebrook
        %%Formula for C(fd)
        CFd =(1/sqrt(f)) + 2*log10(r/(3.7)+ 2.51/(RN*sqrt(f)));
    end
    function CFd1 = colebrook_deriv
        CFd1 = 1/(2*f^(3/2)) + 2.51/RN*f^(3/2)*log(10)*(r/3.7) + 2.51/(RN*f^(1/2));
    end
end

Also check the function for colebrook_deriv i had to make a change (missing '*' i guess) tha you should correct if needed. Problems here:

CFd1 = 1/(2*f^(3/2)) + 2.51/RN*f^(3/2)log(10)(r/3.7) + 2.51/(RN*f^(1/2));
%                                     ^      ^
%                                     |      |
%                                      ----------- Check here

Also i added the final end, because i suspect that you wanted to have nested functions.

MATLAB: I have a problem with the nested function.

Multiple functions way:

x1=input('Enter the x coordinate of the first point ');
y1=input('Enter the y coordinate of the first point ');
x2=input('Enter the x coordinate of the second point ');
y2=input('Enter the y coordinate of the second point ');
x3=input('Enter the x coordinate of the third point ');
y3=input('Enter the y coordinate of the third point ');
[a,b,c]=dist(x1,x2,x3,y1,y2,y3)                         %first function call
s=(a+b+c)/3;
area=calcarea(a,b,c,s)                                  %second function call
fprintf('The area of the triangle is %.2f\n',area) 
function [a,b,c]=dist(x1,x2,x3,y1,y2,y3)   
a=sqrt((x1-x2)^2 + (y1-y2)^2);
b=sqrt((x1-x3)^2 + (y1-y3)^2);
c=sqrt((x2-x3)^2 + (y2-y3)^2);
end
function area=calcarea(a,b,c,s)
area=sqrt(s*(s-a)*(s-b)*(s-c));
end

nested function way:

x1=input('Enter the x coordinate of the first point ');
y1=input('Enter the y coordinate of the first point ');
x2=input('Enter the x coordinate of the second point ');
y2=input('Enter the y coordinate of the second point ');
x3=input('Enter the x coordinate of the third point ');
y3=input('Enter the y coordinate of the third point ');
area=calcarea(x1,x2,x3,y1,y2,y3)                        %parent function call
fprintf('The area of the triangle is %.2f\n',area) 
 function [area]=calcarea(x1,x2,x3,y1,y2,y3)     %parent function
 [a,b,c]=dist(x1,x2,x3,y1,y2,y3) 
 s=(a+b+c)/3;
 area=sqrt(s*(s-a)*(s-b)*(s-c));
 function [a,b,c]=dist(x1,x2,x3,y1,y2,y3)       %nested function
 a=sqrt((x1-x2)^2 + (y1-y2)^2);
 b=sqrt((x1-x3)^2 + (y1-y3)^2);
 c=sqrt((x2-x3)^2 + (y2-y3)^2);
 end
 end

Best Answer

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MATLAB: My code says too many output arguments

MATLAB: I have a problem with the nested function.

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