Double Logarithmic Scale: Find/Create Equation

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Discussion Overview

The discussion revolves around finding or creating an equation for a straight line on a double logarithmic scale graph, specifically focusing on the format of the equation and how to derive it from data points plotted on such a graph.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant seeks assistance in determining the equation for a straight line on a double logarithmic scale graph.
  • Another participant suggests that for a log-log graph, the equation can be expressed as \(\log y = m \cdot \log x + b\), while for a double-log graph, it would be \(y = m \cdot \log \log x + b\).
  • A participant confirms the focus is on the equation \(\log y = m \cdot \log x + b\) and expresses uncertainty about how to generate this equation from a straight line on a log-log graph, particularly regarding the value of \(b\).
  • Another reply emphasizes the importance of having the correct "y" and "x" values for plotting on log-log paper, noting that each coordinate should cover at least one magnitude to potentially yield a straight line.
  • A participant reiterates the need to plot \(\log x\) against \(\log y\) and questions how to determine the value of \(b\) in the context of a straight line equation.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to the problem, with no consensus reached on the method for determining the equation or the value of \(b\).

Contextual Notes

There are limitations regarding the assumptions about data ranges and the appropriateness of using log-log paper, which remain unresolved in the discussion.

Snow178
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double log scale - please help

I am trying to find/create the equation for a straight line on a double logarithmic scale graph - what is the format of the equation or how do I do this using data points from the graph.
 
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If you mean a log-log graph, a straight line would be [itex]\log y=m\cdot\log x + b[/itex]. If you mean a double-log graph, a straight line would be [itex]y = m\cdot\log\log x + b[/itex]. Simplify these as you see fit.
 
Yes - it is for the equation log y= m*logx+b - how do I generate this equation from a straight line on a log-log graph - particularly not sure about b.
 
If the paper is log log, then what you really want is the "y" values for the vertical axis, and the "x" values for the horizontal axis. Each of your coordinates should range over at least one magnitude; otherwise, you probably will not obtain a line. If the result is not a line, then the use of log log paper was probably not the correct choice (but then this is what you are trying to find out). Note carefully, you are plotting the x and y values here on log log paper - NOT their logarithms.
 
Snow178 said:
Yes - it is for the equation log y= m*logx+b - how do I generate this equation from a straight line on a log-log graph - particularly not sure about b.

Well, you plot logx against logy, in the same way that you would plot x against y. If you have an equation for a straight line y=mx+b, what would b be?
 

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