Solved

problem with math.log function in vb.net

Posted on 2008-10-19
4
670 Views
Last Modified: 2010-04-21
I am not sure if I am using the math.log function in vb.net properly.

I am trying to do the formula
%Fat=495/(1.0324-0.19077(log(waist-neck))+0.15456(log(height)))-450
(and converting inches to cm)
with
  LbJP.Text = 495 / (1.0324 - 0.19077 * (Math.Log((Val(TxtWaistBL.Text) * 2.54) - (Val(TxtNeck.Text) * 2.54))) + 0.15456 * (Math.Log((Val(TxtHeight.Text) * 2.54)))) - 450
but the number isn't coming out anywhere near close to where it should.

High points for expediency! I need an answer quickly
0
Comment
Question by:JCM0165
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
4 Comments
 
LVL 16

Expert Comment

by:GreymanMSC
ID: 22754151
The Body Fat Calculation uses base 10 logarithm, where as Math.Log gives the Natural Logarithm.  They are not the same thing.

To convert to base 10 log, you need to divide by the natural log of 10.
  LbJP.Text = 495 / (1.0324 - 0.19077 * (Math.Log((Val(TxtWaistBL.Text) * 2.54)/Math.Log(10) - (Val(TxtNeck.Text) * 2.54))) + 0.15456 * (Math.Log((Val(TxtHeight.Text)/Math.Log(10) * 2.54)))) - 450

Open in new window

0
 
LVL 16

Accepted Solution

by:
GreymanMSC earned 500 total points
ID: 22754162
Duh...
LbJP.Text = 495 / (1.0324 - 0.19077 * (Math.Log((Val(TxtWaistBL.Text) * 2.54) - (Val(TxtNeck.Text) * 2.54))/Math.Log(10)) + 0.15456 * (Math.Log((Val(TxtHeight.Text) * 2.54))/Math.Log(10))) - 450

Open in new window

0
 
LVL 16

Expert Comment

by:GreymanMSC
ID: 22754168
Make sure the bracketing around the logs is in the right place.

The important thing is that:

  Log10(X) = Math.Log(X) / Math.Log(10)
0
 

Author Closing Comment

by:JCM0165
ID: 31507663
Thanks!
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Lots of people ask this question on how to extend the “MembershipProvider” to make use of custom authentication like using existing database or make use of some other way of authentication. Many blogs show you how to extend the membership provider c…
ASP.Net to Oracle Connectivity Recently I had to develop an ASP.NET application connecting to an Oracle database.As I am doing it first time ,I had to solve several problems. This article will help to such developers  to develop an ASP.NET client…

749 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question