Extend a line of best fit
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I have the following code which gives a plot and a line of best fit.
ARI_Weibull = ones(n,1)./P_Weibull;% Average Return Interval 1/P
figure
semilogx((ARI_Weibull), Q, 'r');
p_1 = polyfit(log(ARI_Weibull),Q,1); % Linear best fit
f_1 = polyval(p_1,log(ARI_Weibull));
hold on
semilogx(ARI_Weibull,f_1,'--r')
Q_100yr = polyval(p_1, log(100)) % Q value for 1 in 100 year
xline(100) ;
I now want to extend the line of best fit which I calculated to show its intersection with x = 100, which should correspond to a y value of Q_100yr calculated above.
How do I go about extending this line.
Thanks in advance,
Brian
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KSSV
2020-5-29
You have used polyfit, so you have slope and y-intercept in your hand. For a given value of x, you can find respective y value using polyval.
y_100 = polyval(p_1,100);
If you want to extend to certain range of values [xmin,xmax], also you can do using polyval.
m = 100 ;
xi = linspace(xmin,xmax,m) ; % give your values for xmin, xmax
yi = polyval(p_1,xi);
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