# Solve nonlinear equation with a changing parameter

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Mei Cheng on 12 Sep 2022
Commented: Sam Chak on 12 Sep 2022
Hi,
I am solving the nonlinear equation with a changing parameter (Va), I want to solve the independent variable (x) with a changing parameter (Va).
Then, I want to plot a figure in which the variable is a function of Va, that is,
The nonlinear equation is desribed as below code:
x = linspace(0.1,0.2); % x is an independent variable
% below is a system of nonlinear equations, but only an independent variable
% and an independent changing parameter Va
A = 1.0764e-6./(0.4-2.*x).^3;
B = (0.8308-1.154.*x+0.006.*logA)./(1-(0.2308-1.154.*x).*(0.6+0.006.*logA));
C = 1.2422e-14.*B/(0.4-2.*x).^2;
D = 5.9801e-15.*B;
Va = 5e-5.*(A+C)+7.5e-4.*D;
% Va is a changing parameter, 0.00000001<V<0.01;
% I want to plot a figure in which A as a function of Va
% semilog (Va, A, 'k-')

Sam Chak on 12 Sep 2022
Check if this is the plot you desire:
x = linspace(0.1, 0.2, 101);
A = 1.0764e-6./(0.4-2.*x).^3;
B = (0.8308-1.154.*x+0.006.*log(A))./(1-(0.2308-1.154.*x).*(0.6+0.006.*log(A)));
C = (1.2422e-14.*B)./(0.4-2.*x).^2;
D = 5.9801e-15.*B;
Va = 5e-5.*(A + C) + 7.5e-4.*D;
semilogx(Va, A, 'b-'), grid on, xlabel('V_a'), ylabel('A')
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Sam Chak on 12 Sep 2022
You're welcome, @Mei Cheng.