What is the difference between z[x_]:= D[y[x],x] and z[x_]:=y'[x]?
- To: mathgroup at smc.vnet.net
- Subject: [mg27436] What is the difference between z[x_]:= D[y[x],x] and z[x_]:=y'[x]?
- From: liwen liwen <gzgear at yahoo.com>
- Date: Sun, 25 Feb 2001 20:55:39 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Dear friends,
How are you!
I want to know the difference between z[x_]:=
D[y[x],x] and z[x_]:=y'[x].
Also,I want to why I can not find the answer for the
u[0.5] by the following routine:
(r1[t_] = 93/(1 + 0.12*Cos[3*t]);
d1[t_] := ArcTan[r1[t]/D[r1[t], t]];
Block[{t}, u[t_] := If[(Pi/3 >= t > 0), d1[t]]];
)
u[0.5]
General::"ivar": "\!\(0.5`\) is not a valid variable."
But it is available by the following routine:
(r1[t_] = 93/(1 + 0.12*Cos[3*t]);
d1[t_] = ArcTan[r1[t]/D[r1[t], t]];
Block[{t}, u[t_] := If[(Pi/3 >= t > 0), d1[t]]];
)
u[0.5]
1.22872
(* ------------------------ *)
Please help.
Bets Regards,
Liwen 2/26/2001
E-mail: gzgear at yahoo.com
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