Dear Colleagues,
I have written a simple function which calculates the tangent to a curve at a single point (x1, y1) and in addition using the central difference method, taking points in front and behind the point of interest for comparison against noisy data (due to using the diff function)
As I will be calling this function many times for a large set of input files, I would like to add two additional inputs to the function, a number, 1,...,n which increments the command
figure( insert number here)
and also a string  i.e. device number which updates the title of the figure
h=title('Results for INPUT DEVICE NUMBER HERE')
I would appreciate any help and thank everyone in advance for theory time and suggestions. Apologies if this is trivial but my exposure to MATLAB is limited.
MATLAB R2012B, Windows 7.
The code is as follows:
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function [Central_diff, Exact_point] = Tangent(location, Cdata , Vdata)
%% y = mx + c  Cdata = df*Vdata + C
% Simple central difference approach
y2 = Cdata(location+1);
y1 = Cdata(location1);
x2 = Vdata(location+1);
x1 = Vdata(location1);
y_x = (y2  y1)/(x2x1);
m1 = y_x;
c = Cdata(location)  m1*Vdata(location);
Central_diff = m1*Vdata+c;
% Exact point tangent
y = Cdata;
x = Vdata;
dy = diff(y);
dy = [dy dy(end)];
dx = diff(x);
dx = [dx dx(end)];
df = dy./dx;
m2 = df(location); % gradient at specified location
c = y(location)  x(location)*m2; % y intercept
Exact_point = m2*x + c;
%% Plot figures automatically each time the function is called
figure(1) %replace with string to increment figures per graph generation
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure
SetPlotFont('Times',18); %additional *.m file which must be included
axis auto
set(gca, 'XTick',[8 7 6 5 4 3 2 1 0 1 2 3 4 5 6])
%axis([8 6 0 10e5])
hold all
plot(Vdata, Cdata);
plot(Vdata, Central_diff,'o');
plot(Vdata, Exact_point,'x');
grid on
h=title('CV Curve with Central Difference & Point Tangent INSERT WAFER STRING ');
ylabel('Capacitance')
xlabel('Gate Voltage [V]');
legend('CV Curve','Central Difference Tangent', 'Exact Tangent')
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