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Re: Self-teaching snag

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  • Subject: [mg74598] Re: Self-teaching snag
  • From: dh <dh at>
  • Date: Tue, 27 Mar 2007 04:08:59 -0500 (EST)
  • References: <eu7re0$b6p$>

Hi Todd,

try to figure how many time charge[_] is called when you calculate 


To circumvent this problem, you must save all function values of 

charge[]. This can be done like this:


Now, everything should work as you like.


Todd Allen wrote:

> Hi All,


>    I am trying to refresh my skills in basic problem

> solving using Mathematica, but am running into some

> difficulties which are beginning to make me suspicious

> of Mathematica itself.  (I probably should be

> suspicious of my own brain...but you know how that is

> :-)


> Here is the scenario:  I have written a basic function

> to tell me what percentage of battery power will

> remain in a battery after x number of days, provided

> that we start with a full charge and lose 5% of that

> charge per day.


> If you execute the following code in Mathematica

> (V5.1):


> charge[0]=1.0 (* 100% *);

> charge[day_]:=(charge[day-1]-(0.05*charge[day-1]));

> charge[20]


> I receive an output of 0.358486 for my query at the 20

> day, no problem so far.


> However, when I try to ask for the output at

> charge[35], mathematica seems to enter an endless

> calculation.  I've let the computer run for as long as

> 5 minutes without getting an answer.  Is there

> something wrong with my function, my version of

> Mathematica or something else I haven't considered?



> Additionally,


> When I try the following:


> In[145]:=

> Solve[charge[day]==0.15,day];


> Mathematica gives me the error:

> "$RecursionLimit::reclim: Recursion depth of 256

> exceeded."


> I am trying to ask Mathematica to tell my how many

> days it takes to reduce the battery power to 15

> percent, but I must be messing something up??


> If anyone has any pointers, I'd certainly appreciate

> it, because I am a little stuck right now.


> Best regards,

> Todd Allen




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