I want to find the FWHM (full width at half maximum) of this power density plot. Can someone help me with this matter.

if true
% code end
%%PARAMETERS
D = 10^6;
vi = 10^6;
b = 0.02;
EL = 10^(-10);

%%RANGE
w = linspace(0.9*10^6,1.1*10^6,417);

%%EQUATION
r = 10*10^3;
syms m n;
A = (((D/(4*b))^m)*((2*m*4)+(r/2)))./(factorial(m).*(((2*m*4)+(r/2))^2+(w-vi).^2));
Y = symsum(A, m, 0, 10);
PowerDensity = EL*exp(3).*Y;

%%PLOT
figure;
plot(w-vi, PowerDensity,'red');