Re: New to Mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg126405] Re: New to Mathematica*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Tue, 8 May 2012 04:09:18 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

On 5/6/12 at 8:28 PM, jack.j.jepper at googlemail.com (J.Jack.J.) wrote: >Thanks for replying. Responses embedded: >On May 6, 8:24 am, Murray Eisenberg <mur... at math.umass.edu> wrote: >>First, perhaps folks were reluctant to respond because this looked >>like it could be a homework exercise. >>Second, you don't even have proper Mathematica syntax in your >>equation relating x and k. Did you even try to read the >>documentation to learn the very basics? >I tried and tried for hours but couldn't so much as find any section >that would even tell me how to write the condition that k be an >integer. The specifics of how to specify k is an integer depends on exactly what function you will be using. For several functions such as Integrate, you can use Assuming to specify assumptions about variables. For example, compare: In[12]:= Assuming[{m, n} \[Element] Integers && m != n, Integrate[Cos[n x] Cos[m x], {x, \[Pi], 0}]] Out[12]= 0 with the result obtained with no assumptions about m,n In[13]:= Integrate[Cos[n x] Cos[m x], {x, \[Pi], 0}] Out[13]= (n cos(\[Pi] m) sin(\[Pi] n)-m sin(\[Pi] m) cos(\[Pi] n))/(m^2-n^2) In other cases such as for NMinimize or NMaximize, conditions for variables are specified as part of the syntax. Details can be found in the documentation. But, specifying k is an integer in your particular case really isn't useful. >For example, proper syntax for the equation would be: >>(x/Log[x]) (1 + 1/Log[x]) == 108.2 + k >>Third, the equation itself looks really nasty. Aside from the fact >>that it mixes exact formulas with an approximate real (108.2), the >>left-hand side is transcendental. This is a key point. Typically, transcendental equations do not have closed form symbolic solutions and are only solved numerically. In general, when there is a closed form symbolic solution, it is because the equation occurs often enough in some field someone created a special function to represent the solution. So, assuming the only possible solution is a numerical solution you will have to substitute specific values for k to get a solution such as was done with: >>FindRoot[Evaluate[f[x] /. k -> 2], {x, 1.1}] {x -> 1.11137}

**Follow-Ups**:**Re: New to Mathematica***From:*Andrzej Kozlowski <akozlowski@gmail.com>