Slope of a plotted function in a specified point.

Hi,

I've currently plotted an array signal that displays x and F(x) (not in a continuous manner but in a discreet one as it's an array). The signal plot is shown below.

My question is if there is a way to find out the slope of a point in the plot or if you can somehow get a slope from two close points on the plot, so I can then calculate m (slope constant). I need this in order to find out the transfere function of the signal.

Thank you very much in advance.

Yours faithfully.

Edward.

Answer 1

[Star Strider]

It would be easier to have your data.

Try this:

xv = linspace(0, 5);                                                        % Create Data
yv = sin(2*pi*xv*2.5);                                                      % Create Data

slopefcn = @(xsel,xv,yv) interp1(xv, gradient(yv)./gradient(xv), xsel);     % Interpolate Slope At ‘xsel’
yval = @(xsel,xv,yv) interp1(xv, yv, xsel);                                 % Interpolate ‘yval’ At ‘xsel’

xsel = 2.35;                                                                % Selected ‘X’ Value
ysel = yval(xsel,xv,yv);                                                    % Corresponding ‘Y’ Value

m = slopefcn(xsel, xv, yv);                                                 % Calculate Slope
b = ysel - m*xsel;                                                          % Calculate Y-Intercept (To Draw Line)
calcLine = m*(xsel+[-1 1]*0.05) + b;                                        % Calculate Line For Plot

figure
plot(xv, yv)
hold on
plot(xsel, ysel, '+r')                                                      % Plot Point (Demonstration Only)
plot(xsel+[-1 1]*0.05, calcLine, '-r')                                      % Plot Line (Demonstration Only)
hold off

My code calculates the slope at ‘xsel’ and then plots a line using it in order to demonstrate that it works. That part of the code is not necessary if you do not want to plot a line at the ‘xsel’ point. The data do not need to be regularly-sampled for it to work.