The following error was reported evaluating the function in FunctionLine update: Unable to convert expression containing symbolic variables into double array. Apply 'subs' function first to substitute values for variables.

11 次查看（过去 30 天）

Mehmet Güneri 2020-12-20

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/698380-the-following-error-was-reported-evaluating-the-function-in-functionline-update-unable-to-convert-e

评论： KIPROTICH KOSGEY 2024-7-24

Hi! I am trying to plot a fourier function by using fplot but I am getting the following error.

The following error was reported evaluating the function in FunctionLine update: Unable to convert expression containing symbolic variables into double array.

Apply 'subs' function first to substitute values for variables.

syms f(t) g(t) w;

x=@(t)heaviside(exp(-20*t));

h=@(t) heaviside(12.*t.*exp(55*t));

xf=vpa(fourier(f,t,w));

hf=vpa(fourier(g,t,w));

fplot(@(w) abs(hf), [-20*pi 20*pi])

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Error updating FunctionLine.

The following error was reported evaluating the function in FunctionLine update: Unable to convert expression containing symbolic variables into double array. Apply 'subs' function first to substitute values for variables.

11 个评论
显示 9更早的评论隐藏 9更早的评论

Mehmet Güneri 2020-12-21

I did sir nothing has changed

Rik 2020-12-21

Which function exactly do you want to plot? As Walter mentioned below, you can't plot the idea of a Fourier transform. I expect you want to plot the Fourier transform of either x or h. You don't actually use either in your current code.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Walter Roberson 2020-12-20

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/698380-the-following-error-was-reported-evaluating-the-function-in-functionline-update-unable-to-convert-e#answer_580170

在 MATLAB Online 中打开

fplot(abs(hf), [-20*pi 20*pi])

14 个评论
显示 12更早的评论隐藏 12更早的评论

Torsten 2024-7-23

编辑：Torsten 2024-7-23

在 MATLAB Online 中打开

I don't know how to convert yorder1,...,yorder5 into usual symbolic expressions instead of symbolic functions of x. Maybe you have an idea ...

syms x y(x)

x0 = 0;

y0 = 1;

f = x-y^2;

y1 = f; % First derivative

y2 = diff(y1,x);

y2 = subs(y2,diff(y,x),y1); % Second derivative

y3 = diff(y2,x);

y3 = subs(y3,diff(y,x),y1); % Third derivative

y4 = diff(y3,x);

y4 = subs(y4,diff(y,x),y1); % Fourth derivative

y5 = diff(y4,x);

y5 = subs(y5,diff(y,x),y1); % Fifth derivative

syms h

yorder1 = y0 + h*subs(y1,[x,y(x)],[x0,y0]);

yorder2 = yorder1 + h^2/2*subs(y2,[x,y(x)],[x0,y0]);

yorder3 = yorder2 + h^3/6*subs(y3,[x,y(x)],[x0,y0]);

yorder4 = yorder3 + h^4/24*subs(y4,[x,y(x)],[x0,y0]);

yorder5 = yorder4 + h^5/120*subs(y5,[x,y(x)],[x0,y0]);

subs(y1,[x,y(x)],[x0,y0])

ans(x) =

subs(y2,[x,y(x)],[x0,y0])/2

ans(x) =

subs(y3,[x,y(x)],[x0,y0])/6

ans(x) =

subs(y4,[x,y(x)],[x0,y0])/24

ans(x) =

subs(y5,[x,y(x)],[x0,y0])/120

ans(x) =

eqn = diff(y,x)==f;

cond = y(x0)==y0;

y = dsolve(eqn,cond)

y =

limit(y,x,0,"right")

ans =

vpa(limit(diff(y,x),x,0,"right"))

ans =

vpa(limit(diff(y,x,2),x,0,"right"))/2

ans =

vpa(limit(diff(y,x,3),x,0,"right"))/6

ans =

vpa(limit(diff(y,x,4),x,0,"right"))/24

ans =

vpa(limit(diff(y,x,5),x,0,"right"))/120

ans =

hold on

fplot(real(y),[0 1],'o')

fplot([yorder1(0),yorder2(0),yorder3(0),yorder4(0),yorder5(0)],[0 1])

hold off

grid on

Torsten 2024-7-24

编辑：Torsten 2024-7-24

If you use the Taylor method to solve ordinary differential equations, you won't approximate the solution only once for the initial conditions and take this polynomial as solution over the complete interval of integration as done above. You will use it for a (usually) low order and a small stepsize h to approximate the solution y in x0+h and proceed from there, taking x0 + h and y(x0+h) as new initial conditions.

KIPROTICH KOSGEY 2024-7-24

Thanks for the insights @Torsten, be blessed!

请先登录，再进行评论。

请先登录，再回答此问题。

类别

Mathematics and Optimization Symbolic Math Toolbox Mathematics Calculus

在 Help Center 和 File Exchange 中查找有关 Calculus 的更多信息

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by