# Needs derivative w.r.t. ' y ' & then graph w.r.t ' t '

1 visualizzazione (ultimi 30 giorni)
MINATI il 12 Mag 2019
Commentato: MINATI il 16 Mag 2019
y=0:0.01:5;
P2=5; %%% t=1;
U=exp(y*sqrt(P2)).*(1-erf(y./(2.*sqrt(t))+ sqrt(P2.*t)));
S= - diff(U,y); %%Needs derivative w.r.t. ' y ' & then its value at y=0
F= - diff(U,1);
%%NOW need to graph w.r.t ' t '
t=0:0.01:5;
plot(t,F)
xlabel(' t');
ylabel('F');
While running the code the following error occurs:
The second argument must be a variable or a nonnegative integer specifying the number of differentiations.
Error in
S= - diff(U,y)
And for F= - diff(U,1)
F=[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] is coming which is of no interest.
##### 2 CommentiMostra NessunoNascondi Nessuno
gonzalo Mier il 12 Mag 2019
Can you edit your question to put your code in code format?
Like this
MINATI il 12 Mag 2019
Actually I don't know how to do that

Accedi per commentare.

### Risposta accettata

gonzalo Mier il 12 Mag 2019
Modificato: gonzalo Mier il 12 Mag 2019
diff is a function of the symbolic package, so when you try to derivate U, you are derivating a constant, and by a constant, so F is a 0. To do what you want, you should do it in symbolic and then replace your variable, like:
syms y t
P2=5;
U=exp(y*sqrt(P2)).*(1-erf(y./(2.*sqrt(t))+ sqrt(P2.*t)));
S= - diff(U,y);
v_t=0.01:0.01:5;
F = subs(S,y,0);
plot(v_t,vpa(subs(F,t,v_t)))
xlabel(' t');
ylabel('F');
##### 7 CommentiMostra 5 commenti meno recentiNascondi 5 commenti meno recenti
gonzalo Mier il 15 Mag 2019
Oh sorry, I hope you and your family are ok.
Once a week I just see the answers I have answer that week and clean the ones that were accepted or comment the ones that seems solved. Sorry if it was too soon.
Thank you for accepting my answer and my best wishes for you.
MINATI il 16 Mag 2019
oh Thanks

Accedi per commentare.

### Categorie

Scopri di più su Mathematics in Help Center e File Exchange

### Community Treasure Hunt

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

Start Hunting!

Translated by