Why am I getting "Unrecognized function or variable 'EM'."?

Question

Patrick Kelly 2021-3-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/779632-why-am-i-getting-unrecognized-function-or-variable-em

回答： Arthi Sathyamurthi 2021-3-25

clear all

close all

fxn=@(x,y) (y/x)-0.5*x^2; %Function to work%

exact=@(y) -((x^3)/4)+3*x; %Exact Function%

xini=2; yini=4;

xfin=5;

deltax=[1.0 0.45 0.25];

for i=1:3

d=deltax(i);

[EMx,EMy]=EM(fxn,yini,xini,xfin,d);

[SSHMx,SSHMy]=SSHM(fxn,yini,xini,xfin,d); %Methods Layouts%

[RK2x, RK2y]=RK2(fxn,yini,xini,xfin,d);

[RK4x, RK4y]=RK4(fxn,yini,xini,xfin,d);

fprintf('\nFor Step Size = %2.2g\n' ,d)

for p=1:length(EMx)

a=ext(EMx(p));

e1=abs((a-EMy(a))/a)*100;

e2=abs((a-SSHMy(a))/a)*100; %Error Establishment%

e3=abs((a-RK2y(a))/a)*100;

e4=abs((a-RK4y(a))/a)*100;

fprintf('\t%2.2g\t%g\t%g\t%2.2g\t%g\t%2.2g\t%g\t%2.2g\t%g\t%2.2g\n' ,...

EMx(a),a,EMy(a),e1,SSHMy(a),e2,RK2y(a),e3,RK4y(a),e4)

end

hold on

plot(EMx,EMYy,'LineSpec',2)

plot(SSHMx,SSHMy, 'LineSpec',2)

plot(RK2x,RK2y,'LineSpec',2) %Plot Establishment%

plot(RK4x,RK4y,'LineSpec',2)

plot(RK4x,exact(RK4x), 'LineSpec',3)

ylabel('x')

xlabel('y(x)')

title('x vs y(x) Plot')

legend('Euler Method Soln', 'Heuns Method Soln', 'RK2 Soln', 'RK4 Soln','Exact','location','best')

box on

%Begin Euler's Method%

function [xResult,y1Result] = EulersMethod(g,y0,x0,xfin,d)

N=(xfin-x0)/d;

xn=t0:d:xfin;

y1Result(4)=y0;

xResult(4)=x0;

fprintf('\n\tFor Step Size %2.2g\n', d)

for i=1:length(xn)-1

xResult(i+1)= xResult(i)+d;

y1Result(i+1)= Y1Result(i)+d*double(g(xResult(i),y1Result(i)));

end

%Begin Heun's Method%

function [x,y]=SSHM(g,yi,xi,xf,d)

x(4)=xi;y(4)=yi;

xmax=xf;

xn=xi:d:xmax;

for i=1:length(xn)-1

x(i+1)= x(i)+d;

z1=double(g(x(i),y(i)));

z2=double(g((x(i)+h),(y(i)+h*z1)));

y(i+1)=y(i)+double(d*((z1+z2)/2));

end

%Begin Runge-Kutta 2 Order Method%

function [RKx,RKy]=RK2(g,yini,xini,xfin,d)

x=xini;

y=yini;

xComp=xfin;

n=(xComp-x)/d;

RKx(4)=x;

RKy(4)=y;

for i=1:n

r1=d*g(x,y);

r2=d*g(x+(1/2)*d,y+(1/2)*r1);

dy=r2;

x=x+d;

y=y+dy;

RKx(i+1)=x;

RKy(i+1)=y;

end

%Begin Runge-Kutta 4 Order Method%

function [RKx,RKy]=RK4(g,yini,xini,xfin,d)

x=xini;

y=yini;

xComp=xfin;

n=(xComp-x)/d;

RKx(4)=x;

RKy(4)=y;

for i=1:n

r1=d*double(g(x,y));

r2=d*double(g((x+d/2),(y+r1/2)));

r3=d*double(g((x+d/2),(y+r2/2)));

r4=d*double(g((x+d),(y+r3)));

dy=(1/6)*(r1+2*r2+2*r3+r4);

x=x+d;

y=y+dy;

RKx(i+1)=x;

RKy(i+1)=y;

end

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DGM 2021-3-22

编辑：DGM 2021-3-22

在 MATLAB Online 中打开

It means just what it says. You're referencing the elements of an array that doesn't exist:

[EMx,EMy]=EM(fxn,yini,xini,xfin,d);

It also looks like you have local function definitions in a script. I'm going to assume you're using something newer than R2016b, otherwise that won't work (afaik)

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Answer 1

Arthi Sathyamurthi 2021-3-25

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/779632-why-am-i-getting-unrecognized-function-or-variable-em#answer_657848

在 MATLAB Online 中打开

My initial analysis indicates this error was because the function ‘EM’ is not defined either as a local function nor as a Matlab function. It looks like you misworded the function call. To my understanding it should have been like

[EMx,EMy]=EulersMethod(fxn,yini,xini,xfin,d);

Also the variable t0 has not been initialized in the EulersMethod function.

You can refer to the following page for the possible solutions.

https://www.mathworks.com/help/matlab/matlab_prog/resolve-error-undefined-function-or-variable.html