Using colormap function with area under a curve

Hi,

I would like to know how to use the colormap function. I have used the area function to find the area under the curve now I would like to show that it is changing from 1000 to 100. If I run the code below the area is only blue.

if true
  X = [0.85,0.57,0.42,0.34,0.28,0.24,0.21,0.19,0.17,0.15,0.14,0.13,0.12,0.11,0.10,0.10,0.095,0.09,0.085
Y = 100,150,200,250,300,350,400,450,500,550,600,650,700,750,800,850,900,950,1000
area(X,Y)
grid on
colormap jet
end

I am not sure if this is the correct way to do this so any help is great. Kayne

Answer 1

[Image Analyst]

The colormap function applies a pseudocolor look up table to an image. So you'd have to create an image of that curve using interp1(), then apply the colormap.

[kayne]

I am not quite sure still how to get the image so please bare with me. I think that the variables I was using were confusing me.

I have inserted the code which I have been working from. It calculates the ideal energy from Compressed air using Isothermal process.

clc
clear all
close all
format Short eng
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Define Constants
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Pf  = 100:50:1000;%130*6.8947;       %final in kPa  100:10:
Pi  = 100;%14.7*6.8947;        %final in kPa
R   = 0.287;           %gas constant kJ/kg.K
AT  = 25;            %Temperature Degrees Celcius dC
TK  = 273 + AT;      %Absolute temperature Degrees Kelvin K

% Isothermal Equations which are to be used

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Volumetric energy density using the ideal gas law: 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
V_Isothermal = (R*TK)./Pf;       % Volumetric energy density in m3/kg

Code to get colormap working

    xi= 0.085526:0.041:0.85526; 
    yi = interp1(V_Isothermal,Pf,xi,'cubic');
    plot(V_Isothermal,Pf,'o',xi,yi)

    colormap jet
    X = [xi;yi]'
    image(X)

Which brings up only two colors Red and Blue. What I would like is the colormap to fill in from 1000 (Red) to 100 (blue) for a display.

Thanks Kayne