how to calculate the slope of a line?

I have a data A,B and I want to calculate the slope between two existing points

I want to find the slop between 2012 & 2013 points I try:

 A=[ 234228;   249150 ;  265021  ;281904 ;299862 ];
B=[ 7380; 8045 ;  9903  ;15058 ;13610 ];
plot(A,B);
a = [2010:2014]'; b = num2str(a); c = cellstr(b);
dx = 1; dy = 1; % displacement so the text does not overlay the data points
text(A+dx, B+dy , c)
hold on
coefficients = polyfit(A, B, 1);
slope = coefficients(1);
text(266000,11500,num2str(slope,'y = %.3fx'))

but it seems to be wrong :( ANY IDEA

Answer 1

[Star Strider]

The easiest way is to use the diff funciton. This puts the 2012-2013 slope as the third one in the series:

SlopeBetweenPoints = diff(B)./diff(A)
Slope_2012_2013 = SlopeBetweenPoints(3)

SlopeBetweenPoints =

      44.5651e-003
     117.0689e-003
     305.3367e-003
     -80.6326e-003

Slope_2012_2013 =

     305.3367e-003

EDIT — To print a table:

fprintf(1, '\nSlopes:\n')
fprintf(1, '\t%4d-%4d\t% .4f\n', [a(1:end-1), a(2:end), SlopeBetweenPoints]')

Slopes:
  2010-2011   0.0446
  2011-2012   0.1171
  2012-2013   0.3053
  2013-2014  -0.0806

Answer 2

[John D'Errico]

The slope between consecutive points is simple.

slopes = diff(B)./diff(A);

Pick whatever slope you want from the result. So, here:

A=[ 234228;   249150 ;  265021  ;281904 ;299862 ];
B=[ 7380; 8045 ;  9903  ;15058 ;13610 ];

slopes = diff(B)./diff(A)
slopes =
   0.044565
    0.11707
    0.30534
  -0.080633

slopes(3)
ans =
      0.30534

[Amr Hashem]

Thanks