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

조회 수: 4(최근 30일)
MINATI
MINATI 12 May 2019
댓글: MINATI 16 May 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.

  댓글 수: 2

gonzalo Mier
gonzalo Mier 12 May 2019
Can you edit your question to put your code in code format?
Like this
MINATI
MINATI 12 May 2019
Actually I don't know how to do that

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채택된 답변

gonzalo Mier
gonzalo Mier 12 May 2019
편집: gonzalo Mier 12 May 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');

  댓글 수: 7

표시 이전 댓글 수: 4
MINATI
MINATI 15 May 2019
Sorry for accepting the answer late
We had a very bad CYCLONE, So we had no electricity and no internet for last days
Thats why I accepted late
gonzalo Mier
gonzalo Mier 15 May 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
MINATI 16 May 2019
oh Thanks

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