Finding slope from a 2D plot

107 次查看（过去 30 天）

adrooney 2014-12-7

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/165733-finding-slope-from-a-2d-plot

评论： Image Analyst 2014-12-7

I have plotted a group of points using plot(x,y) command. The plot is non linear. I attached a picture with a line drawn on the linear side of the graph. Give me an idea of how to find the slope.

2 个评论
显示无隐藏无

Star Strider 2014-12-7

Obvious question: Slope of what ?

Four possibilities:

The slope of the line from about 0 to about 0.5 ...
The slope of the relatively linear descending part of the curve between about 1 and 3.75 ...
The descending part of the loop ...
The ascending part of the loop ...

... or something else?

adrooney 2014-12-7

sorry to draw the line. I'm attaching a picture with the line.(it is on the ascending part of the loop). What I have done is created a dummy point in the third quadrant and drew the line. I need to find the slope and intersection. Can I do it in matlab?

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Image Analyst 2014-12-7

5
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/165733-finding-slope-from-a-2d-plot#answer_161563

在 MATLAB Online 中打开

I see 4 lines. Anyway, extract the x and y coordinates that you want to fit a line to, then use polyfit:

coefficients = polyfit(x, y, 1);
% Now get the slope, which is the first coefficient in the array:
slope = coefficients(1);

6 个评论
显示 4更早的评论隐藏 4更早的评论

adrooney 2014-12-7

Ok thanks I'll try doing that. One more doubt can't we plot grid lines on the plot and all the four quadrants?

Image Analyst 2014-12-7

在 MATLAB Online 中打开

You can use

grid on;

or you can use line() to draw lines at certain, specific places.

xl = xlim();
yl = ylim();
% Draw quadrant dividing lines
xLine = (x(1)+x(2))/2;
yLine = (y(1)+y(2))/2;
% Draw vertical line
line([xLine, xLine], yl, 'Color', 'r', 'LineWidth', 2);
% Draw horizontal line.
line(xl, [yLine, yLine], 'Color', 'r');