How do I plot my code? I got Blank Graph
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hgrlk
am 14 Apr. 2019
Kommentiert: Geoff Hayes
am 15 Apr. 2019
Hello,
I want to plot my code. It's newton-raphson method code. But I musn't change the while loop. In the question it is given that "use while and if statement".
When I write the plot, Matlab gives me a blank graph. So I exclude the " plot" when I'm sharing the code with you.
NOTE : . I want 2 graphs, one is f(x) versus i and one is x versus i. Also how can I write a function for the circle mark for each data point in the function?
( I use Matlab R2015a )
Thank You.!!
clc
clear all
close all
fprintf('%10s %10s %10s %10s %10s\n','i','xi','f(xi)','diff_f(xi)','|Ea|')
Ea = 100;
m = 0 ;
x = 0;
while abs(Ea) > 10^(-3)
if m <= 50
f = @(x) x^3 - x - 3 ;
diff = @(x) 3*(x^2) - 1 ;
xnew = x - (f(x) / diff(x));
Ea = (((xnew-x)/xnew)*100);
fprintf('%10.4f %10.4f %10.4f %10.4f %10.4f\n',m,x,f(x),diff(x),abs(Ea))
x = xnew;
else
break
end
m = m+1;
end
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Geoff Hayes
am 14 Apr. 2019
hgrlk - store each value of x from each iteration of your loop. Then, when the loop concludes, you can plot the data. Perhaps somethig like
Ea = 100;
maxIterations = 50;
m = 1;
x = zeros(maxIterations,1);
x(m) = 12;
f = @(x) x.^3 - x - 3 ;
diff = @(x) 3*(x.^2) - 1 ;
while abs(Ea) > 10^(-3) && m < maxIterations
xnew = x(m) - (f(x(m)) / diff(x(m)));
Ea = (((xnew-x(m))/xnew)*100);
fprintf('%d %10.4f %10.4f %10.4f %10.4f\n',m,x(m),f(x(m)),diff(x(m)),abs(Ea));
m = m + 1;
x(m) = xnew;
end
x = x(1:m);
figure;
plot(x);
figure;
plot(f(x));
Note how we combine the two conditions that you have - that for the error and that for the maximum number of iterations. The f and diff are defined outside of the while loop since we can then have access to f when we plot (once complete). On each iteration of the loop, we store the new estimate in an array so that we can plot all values of x and f(x). See plot LineSpec properties for details on how to add colour, style, and markers to your plot.
2 Kommentare
Geoff Hayes
am 15 Apr. 2019
You can put the if back then if that is what you need (same as you originally had). As for nothing in the graph, I was able to see the results plotted in each figure (using the code I posted).
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