I need to save my output into an array so i can plot my results

Hi I wrote the following function so that it could be used in general

function [fprimeapprox1,fprimeapprox2]= threepointformula(Fun,FunPrime)

disp('        t          f(t)        fprimeexact     fprimeapprox1     Error    fprimeapprox2      Error ')
for t=0:0.1:2.5
    h=0.1;
    fexact=feval(Fun,t);
    fprimeexact= feval(FunPrime,t);
    fprimeapprox1= (1/(2*h))*((feval(Fun,t+h)-feval(Fun,t-h)));
    fprimeapprox2= (1/(2*h))*(-3*feval(Fun,t)+4*feval(Fun,t+h)-feval(Fun,t+2*h));
    ErrorOf1= abs(fprimeexact-fprimeapprox1);
    ErrorOf2= abs(fprimeexact-fprimeapprox2);
    fprintf('\t%f  \t%f      \t%f     \t%f      \t%f   \t%f     \t%f  \n',t,fexact,fprimeexact,fprimeapprox1,ErrorOf1,fprimeapprox2,ErrorOf2)

end

and then a script that calls it

clc
u= @(x) exp(-x).*cos(5.*x);
v= @(x) -5*exp(-x).*sin(5.*x)-exp(-x).*cos(5*x);
Y= threepointformula(u,v);

so my issue is that in the function i need to save fexact fprimeexact fprimeapprox1 and fprimeapprox2 into an array so i can graph it vs t. I've seen a lot of people make a zeros vector and start adding them in but my increments aren't by positive integers any help would be greatly appreciated thank you.

Answer 1

[Eric]

function [t,FE,FPE,FPAX1,FPAX2,ErrorOf1,ErrorOf2]= threepointformula(Fun,FunPrime)
t=0:0.1:2.5;
FE=zeros(length(t),1);
FPE=zeros(length(t),1);
FPAX1=zeros(length(t),1);
FPAX2=zeros(length(t),1);
for i=1:length(t)
    h=0.1;
    fexact=feval(Fun,t(i));
    FE(i)=fexact;
    fprimeexact= feval(FunPrime,t(i));
    FPE(i)=fprimeexact;
    fprimeapprox1= (1./(2.*h)).*((feval(Fun,t(i)+h)-feval(Fun,t(i)-h)));
    FPAX1(i)=fprimeapprox1;
    fprimeapprox2= (1./(2.*h)).*(-3.*feval(Fun,t(i))+4.*feval(Fun,t(i)+h)-feval(Fun,t(i)+2.*h));
    FPAX2(i)=fprimeapprox2;

end
ErrorOf1= abs(FPE-FPAX1);
ErrorOf2= abs(FPE-FPAX2);

to call the function

clc
clear all
u= @(x) exp(-x).*cos(5.*x);
v= @(x) -5*exp(-x).*sin(5.*x)-exp(-x).*cos(5*x);
[t,FE,FPE,FPAX1,FPAX2,ErrorOf1,ErrorOf2]= threepointformula(u,v);
DISP=[t',FE,FPE,FPAX1,ErrorOf1,FPAX2,ErrorOf2];
disp('       t        FE       FPE      FPAX1      Error    FPAX2     Error')
disp(DISP)
plot(t,FE)

Answer 2

[KSSV]

function [T,FE,FPE,FPAX1,FPAX2]= threepointformula(Fun,FunPrime)
disp('        t          f(t)        fprimeexact     fprimeapprox1     Error    fprimeapprox2      Error ')
T = 0:0.1:2.5 ;
FE = zeros(length(T),1) ;
FPE = FE ;
FPAX1 = FE ;
FPAX2 = FE ;

for i=1:length(T)
    t = T(i) ;
    h=0.1;
    fexact=feval(Fun,t);
    fprimeexact= feval(FunPrime,t);
    fprimeapprox1= (1/(2*h))*((feval(Fun,t+h)-feval(Fun,t-h)));
    fprimeapprox2= (1/(2*h))*(-3*feval(Fun,t)+4*feval(Fun,t+h)-feval(Fun,t+2*h));
    ErrorOf1= abs(fprimeexact-fprimeapprox1);
    ErrorOf2= abs(fprimeexact-fprimeapprox2);
    fprintf('\t%f  \t%f      \t%f     \t%f      \t%f   \t%f     \t%f  \n',t,fexact,fprimeexact,fprimeapprox1,ErrorOf1,fprimeapprox2,ErrorOf2)
    FE(i) = fexact ;
    FPE(i) = fprimeexact ;
    FPAX1(i) = fprimeapprox1 ;
    FPAX2(i) = fprimeapprox2 ;

end
size(fexact)

Call the function by:

u= @(x) exp(-x).*cos(5.*x);
v= @(x) -5*exp(-x).*sin(5.*x)-exp(-x).*cos(5*x);
[T,FE,FPE,FPAX1,FPAX2] = threepointformula(u,v);

plot(T,FE,'r') ;
hold on
plot(T,FPE,'b') ;
plot(T,FPAX1,'m') ;
plot(T,FPAX2,'c') ;
legend('exact' , 'prime exact','appx.1','appx.2')

Note that code can be simplified.

[Eric]

so when i ran this code it no longer prints out the values in columns like the one i wrote does it only prints out the last values when t=2.5

[KSSV]

No change is made at the print part....only after printing it is saved in the array.

[Eric]

also if i ask it to show me FE its just a vector of 0's except the last row

[KSSV]

I have plotted it at the end. Plot is coming out non zeros.

[Eric]

the plot is wrong as well it should be a cos graph not what you get when that code is runned