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Specifically, a straight line on a log–log plot containing points (x 0, F 0) and (x 1, F 1) will have the function: = (/) (/), Of course, the inverse is true too: any function of the form = will have a straight line as its log–log graph representation, where the slope of the line is m.
The simplest is the slope-intercept form: = +, from which one can immediately see the slope a and the initial value () =, which is the y-intercept of the graph = (). Given a slope a and one known value () =, we write the point-slope form:
where is the slope and is the y-intercept. Because this is a function of only x {\displaystyle x} , it can't represent a vertical line. Therefore, it would be useful to make this equation written as a function of both x {\displaystyle x} and y {\displaystyle y} , to be able to draw lines at any angle.
On a log–linear plot (logarithmic scale on the y-axis), pick some fixed point (x 0, F 0), where F 0 is shorthand for F(x 0), somewhere on the straight line in the above graph, and further some other arbitrary point (x 1, F 1) on the same graph.
In two dimensions, the equation for non-vertical lines is often given in the slope-intercept form: = + where: m is the slope or gradient of the line. b is the y-intercept of the line. x is the independent variable of the function y = f(x).
Using this form, vertical lines correspond to equations with b = 0. One can further suppose either c = 1 or c = 0, by dividing everything by c if it is not zero. There are many variant ways to write the equation of a line which can all be converted from one to another by algebraic manipulation. The above form is sometimes called the standard form.
We can see that the slope (tangent of angle) of the regression line is the weighted average of (¯) (¯) that is the slope (tangent of angle) of the line that connects the i-th point to the average of all points, weighted by (¯) because the further the point is the more "important" it is, since small errors in its position will affect the ...
A set of pairs , making a rectangular grid is typically used for the drawing. An isocline (a series of lines with the same slope) is often used to supplement the slope field. In an equation of the form y ′ = f ( x , y ) {\displaystyle y'=f(x,y)} , the isocline is a line in the x , y {\displaystyle x,y} -plane obtained by setting f ( x , y ...