Re: managing order of magnitude instead of numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg56703] Re: [mg56672] managing order of magnitude instead of numbers*From*: Chris Chiasson <chris.chiasson at gmail.com>*Date*: Wed, 4 May 2005 00:33:31 -0400 (EDT)*References*: <200505030926.FAA25648@smc.vnet.net>*Reply-to*: Chris Chiasson <chris.chiasson at gmail.com>*Sender*: owner-wri-mathgroup at wolfram.com

Assuming you have defined an order of magnitude function, (don't call it O.. that is a reserved symbol).. have it return the result wrapped in a special head (again, don't call it O). You could use upvalues to determine that the subtraction of two orders of magnitude is equal to the greater order of magnitude. In[3]:= TagSet[ODM,ODM[a_]-ODM[b_],ODM[Max[a,b]]] Out[3]= ODM[Max[a,b]] In[9]:= ODM[5]-ODM[1] Out[9]= ODM[5] On 5/3/05, foice <foice@n0nspammar&tiscali.it> wrote: > i need to make calculation without specifing the exact values of my > parameters, i want only to specify their order of magnitude. > obviously i need only order of magnitudes as result. > > now the problem is that > > O(1) - O(1) = O(1) > > while > > 1-1 = 0 > > so it's clear i cannot use numbers to make this "order of magintude > calculation" > > at the present stage i let mathematica do the calculation in a fully > simbolic way and then, by hand calculation, i get my result by > susbstitution of the order of magnitudes in place of the symobls used. > > making a very simple example: > > i ask to mathematica to do > > a - b > > and then i substitute > > a=O(1) > > b=O(0.002) > > and calculate > > a - b = O(1) > > in this way i'm making operation between magnitues not values, but i > have to do it on my own, while doing calculation with mathematica will > be much better. > > is there any way to make calculation betwwen order of magnitues > instead of between numbers? > > thanks. > roberto. > > -- Chris Chiasson http://chrischiasson.com/ 1 (810) 265-3161

**References**:**managing order of magnitude instead of numbers***From:*foice <foice@N0NSPAMMAR&tiscali.it>