How to calculate Area under a curve (negatif side)

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Ceren Memis
Ceren Memis 2022-1-24
评论： Star Strider 2022-1-26
I have a dataset and I made it curve. I want to calculate the area (like result_2) of ​​the curve but I get a result like the picture on the result_1. Is there anyone who can help with this issue?
f = [-0.390930468901234 -0.346778353936444 -0.304499753808231 -0.264063453713497 -0.225438238849140 -0.188592894412060 -0.153496205599158 -0.120116957607333 -0.0884239356334846 -0.0583859248745134 -0.0299717105273190 -0.00315007778880116 0.0221101881441402 0.0458403020746052 0.0680714788056940 0.0888349331405067 0.108161879882144 0.126083533833705 0.142631109798290 0.157835822579000 0.171728886978934 0.184341517801193 0.195704929848877 0.205850337925086 0.214808956832921 0.222612001375480 0.229290686355865 0.234876226577176 0.239399836842512 0.242892731954974 0.245386126717662 0.246911235933676 0.247499274406116 0.247181456938083 0.245988998332677 0.243953113392996 0.241105016922143 0.237475923723217 0.233097048599318 0.227999606353545 0.222214811789001 0.215773879708783 0.208708024915994 0.201048462213732 0.192826406405098 0.184073072293192 0.174819674681114 0.165097428371965 0.154937548168844 0.144371248874851 0.133429745293087 0.122144252226652 0.110545984478646 0.0986661568521688 0.0865359841503211 0.0741866811762028 0.0616494627329141 0.0489555436235550 0.0361361386512258 0.0232224626190266 0.0102457303300567 -0.00276284341258221 -0.0157720438057912 -0.0287506560464691 -0.0416674653315173 -0.0544912568578337 -0.0671908158223202 -0.0797349274218757 -0.0920923768533994 -0.104231949313792 -0.116122429999953 -0.127732604108783 -0.139031256837181 -0.149987173382047 -0.160569138940281 -0.170745938708783 -0.180486357884452 -0.189759181664190 -0.198533195244895 -0.206777183823467 -0.214459932596806 -0.221550226761814 -0.228016851515387 -0.233828592054427 -0.238954233575834 -0.243362561276507 -0.247022360353347 -0.249902416003253 -0.251971513423126 -0.253198437809864 -0.253551974360368 -0.253000908271538 -0.251514024740273 -0.249060108963473 -0.245607946138040 -0.241126321460871 -0.235584020128867 -0.228949827338928 -0.221192528287954 -0.212280908172844]
t = linspace(0,100,100);
sinus_f = sin(f)
plot(t,sinus_f)
min_f = find(islocalmin(sinus_f));
max_f = find(islocalmax(sinus_f));
axis tight
P1_1 = gca; % gca creates a cartesian axes object
P1_1.XAxisLocation = 'origin'
hold on
basevalue_A1 = 1;
xline(t(min_f),'--b')
yline(sinus_f(min_f),'--r')
xline(t(max_f),'--b')
yline(sinus_f(max_f),'--r')
area_A1 = area(t(max_f:min_f),sinus_f(max_f:min_f),'FaceColor','g') % the area by points

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Star Strider
Star Strider 2022-1-24
编辑：Star Strider 2022-1-24
Ran in:
I went with the patch function because I’m more familiar with it.
Try ths —
f = [-0.390930468901234 -0.346778353936444 -0.304499753808231 -0.264063453713497 -0.225438238849140 -0.188592894412060 -0.153496205599158 -0.120116957607333 -0.0884239356334846 -0.0583859248745134 -0.0299717105273190 -0.00315007778880116 0.0221101881441402 0.0458403020746052 0.0680714788056940 0.0888349331405067 0.108161879882144 0.126083533833705 0.142631109798290 0.157835822579000 0.171728886978934 0.184341517801193 0.195704929848877 0.205850337925086 0.214808956832921 0.222612001375480 0.229290686355865 0.234876226577176 0.239399836842512 0.242892731954974 0.245386126717662 0.246911235933676 0.247499274406116 0.247181456938083 0.245988998332677 0.243953113392996 0.241105016922143 0.237475923723217 0.233097048599318 0.227999606353545 0.222214811789001 0.215773879708783 0.208708024915994 0.201048462213732 0.192826406405098 0.184073072293192 0.174819674681114 0.165097428371965 0.154937548168844 0.144371248874851 0.133429745293087 0.122144252226652 0.110545984478646 0.0986661568521688 0.0865359841503211 0.0741866811762028 0.0616494627329141 0.0489555436235550 0.0361361386512258 0.0232224626190266 0.0102457303300567 -0.00276284341258221 -0.0157720438057912 -0.0287506560464691 -0.0416674653315173 -0.0544912568578337 -0.0671908158223202 -0.0797349274218757 -0.0920923768533994 -0.104231949313792 -0.116122429999953 -0.127732604108783 -0.139031256837181 -0.149987173382047 -0.160569138940281 -0.170745938708783 -0.180486357884452 -0.189759181664190 -0.198533195244895 -0.206777183823467 -0.214459932596806 -0.221550226761814 -0.228016851515387 -0.233828592054427 -0.238954233575834 -0.243362561276507 -0.247022360353347 -0.249902416003253 -0.251971513423126 -0.253198437809864 -0.253551974360368 -0.253000908271538 -0.251514024740273 -0.249060108963473 -0.245607946138040 -0.241126321460871 -0.235584020128867 -0.228949827338928 -0.221192528287954 -0.212280908172844]
f = 1×100
-0.3909 -0.3468 -0.3045 -0.2641 -0.2254 -0.1886 -0.1535 -0.1201 -0.0884 -0.0584 -0.0300 -0.0032 0.0221 0.0458 0.0681 0.0888 0.1082 0.1261 0.1426 0.1578 0.1717 0.1843 0.1957 0.2059 0.2148 0.2226 0.2293 0.2349 0.2394 0.2429
t = linspace(0,100,100);
sinus_f = sin(f)
sinus_f = 1×100
-0.3810 -0.3399 -0.2998 -0.2610 -0.2235 -0.1875 -0.1529 -0.1198 -0.0883 -0.0584 -0.0300 -0.0032 0.0221 0.0458 0.0680 0.0887 0.1080 0.1257 0.1421 0.1572 0.1709 0.1833 0.1945 0.2044 0.2132 0.2208 0.2273 0.2327 0.2371 0.2405
plot(t,sinus_f)
min_f = find(islocalmin(sinus_f));
max_f = find(islocalmax(sinus_f));
axis tight
P1_1 = gca; % gca creates a cartesian axes object
P1_1.XAxisLocation = 'origin'
P1_1 =
Axes with properties: XLim: [0 100] YLim: [-0.3810 0.2450] XScale: 'linear' YScale: 'linear' GridLineStyle: '-' Position: [0.1300 0.1100 0.7750 0.8150] Units: 'normalized' Show all properties
hold on
basevalue_A1 = 1;
xline(t(min_f),'--b')
yline(sinus_f(min_f),'--r')
xline(t(max_f),'--b')
yline(sinus_f(max_f),'--r')
Lv = t<=t(min_f) & t>=t(max_f);
AUC = trapz(t(Lv), sinus_f(Lv));
text(40, -0.1, sprintf('AUC = %.6f', AUC))
area_A1 = patch([t(Lv) flip(t(Lv))], [ones(size(t(Lv)))*sinus_f(min_f) flip(sinus_f(Lv))], 'g', 'FaceAlpha',0.25);
% area_A1 = area(t(max_f:min_f),sinus_f(max_f:min_f),'FaceColor','g') % the area by points
EDIT — (24 Jan 2022 at 18:18)
Added ‘AUC’ calculation and text display.
.
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Ceren Memis
Ceren Memis 2022-1-26
Now I got exactly the result I wanted. Thank you so much.

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