how to make something between quotation automatic!

I want to make 'poly2' automatic by changing n? How can I do this using for example eval function?

n=2;% 3,4,....
f1 = fit(x,y,'poly2')

Answer 1

[Steven Lord]

If you're just fitting polynomials you could use polyfit and polyval, specifying n as the third input argument.

load census
n = 2;
[p, s] = polyfit(cdate, pop, n);
plot(cdate, pop, 'o', cdate, polyval(p, cdate, s), '-')

But you can also use fit if you want. There's no need to use eval here, just use string + or char manipulation.

theFit = fit(cdate, pop, "poly" + n, 'Normalize', 'on') % or

theFit = 
     Linear model Poly2:
     theFit(x) = p1*x^2 + p2*x + p3
       where x is normalized by mean 1890 and std 62.05
     Coefficients (with 95% confidence bounds):
       p1 =       25.18  (23.58, 26.79)
       p2 =       75.43  (74.04, 76.83)
       p3 =       61.74  (59.7, 63.79)

theFit2 = fit(cdate, pop, ['poly', num2str(n)], 'Normalize', 'on') % or

theFit2 = 
     Linear model Poly2:
     theFit2(x) = p1*x^2 + p2*x + p3
       where x is normalized by mean 1890 and std 62.05
     Coefficients (with 95% confidence bounds):
       p1 =       25.18  (23.58, 26.79)
       p2 =       75.43  (74.04, 76.83)
       p3 =       61.74  (59.7, 63.79)

theFit2 = fit(cdate, pop, sprintf('poly%d', n), 'Normalize', 'on')

theFit2 = 
     Linear model Poly2:
     theFit2(x) = p1*x^2 + p2*x + p3
       where x is normalized by mean 1890 and std 62.05
     Coefficients (with 95% confidence bounds):
       p1 =       25.18  (23.58, 26.79)
       p2 =       75.43  (74.04, 76.83)
       p3 =       61.74  (59.7, 63.79)

figure
plot(cdate, pop, 'o')
hold on
plot(theFit, '-')

[Ham Man]

Steven thank you so much for nice explanation with many choices. Much appreciated!