Re: Issue with Sum Version7

• To: mathgroup at smc.vnet.net
• Subject: [mg95637] Re: Issue with Sum Version7
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Fri, 23 Jan 2009 05:08:27 -0500 (EST)

```On 1/22/09 at 7:05 AM, bghekaya at gmail.com wrote:

>Anyone seen this:

>In[120]:= Sum[i, {i, 0, 99999, .1}]

>Out[120]= 4.99991*10^10

>In[121]:= Sum[i, {i, 0, 100000, .1}]

>Out[121]= Sum[i, {i, 0, 100000, 0.1}]

>On Mac OS X 10.5.6

I get the same result. But this result is easily avoided by either

In[3]:= NSum[i, {i, 0, 100000, .1}]

Out[3]= 5.00001*10^10

or

In[4]:= Sum[i, {i, 0, 100000, 1/10}]

Out[4]= 50000050000

The general rule in Mathematica is when working with machine

The key advantage of Sum over NSum is being able to return
symbolic answers for simple problems. Note

In[7]:= Sum[n, {n, 0, k, a}]

Out[7]= (k (a+k))/(2 a)

returns nearly instantly, much faster than doing the explicit sum.

Compare

In[1]:= Sum[n, {n, 0, 100000, 1/10}] // Timing

Out[1]= {0.135397,50000050000}

In[2]:= Sum[n, {n, 0, k, a}] /. {a -> 1/10, k -> 100000} // Timing

Out[2]= {0.018729,50000050000}

Of course none of this changes the fact there appears to be a
problem with Sum.

```

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