[Date Index]
[Thread Index]
[Author Index]
Re: Problem with DSolve
*To*: mathgroup at smc.vnet.net
*Subject*: [mg96476] Re: [mg96410] Problem with DSolve
*From*: Daniel Lichtblau <danl at wolfram.com>
*Date*: Sat, 14 Feb 2009 03:10:54 -0500 (EST)
*References*: <200902130841.DAA26548@smc.vnet.net>
Tony wrote:
> can anyone help what is wrong?
> On version 7 I enter
>
> DSolve[{y'[x]==.02*y[x]-y[x]^2,y[0]==a},y[x],x]
>
> and get
>
> During evaluation of In[58]:= Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; use Reduce for complete solution information. >>
> During evaluation of In[58]:= Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; use Reduce for complete solution information. >>
> During evaluation of In[58]:= DSolve::bvnul: For some branches of the general solution, the given boundary conditions lead to an empty solution. >>
You can see all calls to Solve, as below.
In[12]:= Solve[a___] := Null /; (Print[InputForm[solve[a]]]; False)
In[13]:= DSolve[{y'[x]==.02*y[x]-y[x]^2,y[0]==a},y[x],x]
solve[-0.02*y[x] + 1.*y[x]^2 + 1.*Derivative[1][y][x] == 0,
> Derivative[1][y][x]]
solve[-Log[y[x]] + Log[-1 + 50*y[x]] == -x/50 + C[1], y[x]]
solve[{(1. - 50.*a + 1.*2.718281828459045^C[1]*a)/
> (50. - 1.*2.718281828459045^C[1]) == 0}, {C[1]},
> VerifySolutions -> True]
Solve::ifun: Inverse functions are being used by Solve, so some
solutions may
not be found; use Reduce for complete solution information.
0.02 x
2.71828
Out[13]= {{y[x] -> -------------------------------------------}}
0.02 x -1. (1. - 50. a) 1.
50. 2.71828 - 1. (----------------)
a
The one that gives rise to the message involves solving for the
constant, and it appears in exponents. Hence the warning message.
Daniel Lichtblau
Wolfram Research
Prev by Date:
**Re: testing if a point is inside a polygon**
Next by Date:
**Re: Re: (2/3)[[1]]**
Previous by thread:
**Problem with DSolve**
Next by thread:
**Re: Problem with DSolve**
| |