Use a custom baseline to calculate area of a graph
조회 수: 3 (최근 30일)
이전 댓글 표시
Hi,
I am a beginner level Matlab user. I tried searching the forum, could not find a working answer for this quesiton
I have this graph of Heat Flow vs Time. I need to calculate the mathematical area (Area above the baseline being positive and area below being negative) under the curve with a straight baseline formed between first and the last x-value (which is user defined) as shown in the figure below. At present, i am using the following code
%this limit we defined before is passed on to the trapz function to
lims = (x2_values >=value_of_interest_1)&(x2_values <=value_of_interest_2);
%perform numerical integration using the trapeoidal method
net_heat_flow = trapz(x2_values(lims), y2_values(lims));
However, this code calculates the area based on zero baseline. So, my question is how can i define a custom baseline as a straight line formed between the two points of interest? Can this be done using Matlab?
The figure below is from custom software I am using. However, I am trying to use Matlab for this because there are over 500 data files i need to process.
Thanks. Any help or suggestion is appreciated.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/642275/image.png)
댓글 수: 0
채택된 답변
Star Strider
2021년 6월 4일
Use trapz to calculate the area under the curve, and use trapz separately to calculate the area under the line.
Then subtract them.
Example —
x = linspace(0,10); % X-Vector
y = 2.5*sinc(x-5) - 0.2*x; % Y-Vector
sincarea = trapz(x, 2.5*sinc(x-5)) % Area Under Original Curve (Reference)
yarea = trapz(x,y) % Area Under Displayed Curve
linearea = trapz(x, -0.2*x) % Area Under The Line
curvearea = yarea - linearea % Area Between Line And Curve
figure
plot(x, y)
hold on
plot(x, -0.2*x)
hold off
grid
axis('equal')
.
댓글 수: 2
Star Strider
2021년 6월 7일
My pleasure!
If I understand your comment correctly, yes.
It returns the area between the x-axis (at y=0) and the line as ‘linearea’, and the area between the x-axis and the curve as ‘yarea’ separately, then subtracts them to return ‘curvearea’. (The ‘sincarea’ calculation is not necessary for the code, other than serving as a sort of ‘proof’ tthat the code returns the correct result.)
.
추가 답변 (0개)
참고 항목
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!