Solved

problem with math.log function in vb.net

Posted on 2008-10-19
4
662 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
  • 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

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

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

I have developed many web applications with asp & asp.net and to add and use a dropdownlist was always a very simple task, but with the new asp.net, setting the value is a bit tricky and its not similar to the old traditional method. So in this a…
I recently went through the process of creating a Calendar Control of events with the basis of using a database to keep track of the dates that are selectable, one requirement was to have the selected date pop-up in a simple lightbox.  At first this…
This Micro Tutorial demonstrates using Microsoft Excel pivot tables, how to reverse engineer competitors' marketing strategies through backlinks.
Internet Business Fax to Email Made Easy - With eFax Corporate (http://www.enterprise.efax.com), you'll receive a dedicated online fax number, which is used the same way as a typical analog fax number. You'll receive secure faxes in your email, fr…

895 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

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now