函数或变量 'poly2str' 无法识别，如何导入poly2str?

x=-2*pi:pi/2:2*pi;

y=[1,0,-1,0,1,0,-1,0,1];

p2=polyfit(x,y,2);

p3=polyfit(x,y,3);

p4=polyfit(x,y,4);

p6=polyfit(x,y,6);

disp('二次拟合函数'),f2=poly2str(p2,'x');

disp('三次拟合函数'),f3=poly2str(p3,'x');

disp('四次拟合函数'),f4=poly2str(p4,'x');

disp('七次拟合函数'),f6=poly2str(p6,'x');

x1=-2*pi:pi/10:2*pi;

y2=polyval(p2,x1);

y3=polyval(p3,x1);

y4=polyval(p4,x1);

y6=polyval(p6,x1);

yy=cos(x1);

plot(x,y,x1,y2,'-b',x1,y3,'-.r',x1,y4,'*c',x1,y6,'.g',x1,yy);

Answer 1

[Yash]

Hi Ran,

我会用英语回答

I understand that you want to use "poly2str" function to return polynomial as string. I tried reproducing the error "Unrecognized function or variable 'poly2str'" on my end. However, I didn't encounter any error. Consider running the following command in the MATLAB command window to check if "poly2str.m" is present on the root path:

>> which poly2str -all

If "poly2str.m" is not found by "which", then consider running the following command in the MATLAB command window to refresh function and file system path cache:

>> rehash toolboxcache

If "poly2str.m" is still not found by "which", then verify if "Control System" toolbox is installed or not. Refer here for more information on installing a toolbox: https://www.mathworks.com/matlabcentral/answers/101885-how-do-i-install-additional-toolboxes-into-an-existing-installation-of-matlab

Alternatively, consider using the function "poly2sym" to create symbolic polynomial from vector of coefficients. Refer here for more information on "poly2sym" function: https://www.mathworks.com/help/releases/R2023a/symbolic/sym.poly2sym.html

>> p = poly2sym([0.75, -0.5, 0.25])
 
p =
 
(3*x^2)/4 - x/2 + 1/4

I hope this helps!

[Ran]

Thank you very much!It helps me a lot and solves my homework i have been struggling with.

[慧敏]

请问最后是怎么解决的？