Intercept of each line to y-line

Hello folks,

I am making curve fit plot for some data and trying to make intercept point of each data line with y-line.

For examples. each line should give intercept point so there will be 10 intercept points which can be stored in any array.

I am concerning only x-axis value in the x-yline(1.5228, '--') intercept values. I tried with intercept commands but the problem is here I am dealing with objects.

I am share here code. please have a look and help in this regard, so that when I run a code it will provides x-y intercept values.

clear
close all

Data=[
0.11	0.3	0.28	0.6	0.31
0.23	0.78	0.57	1.08	0.43
0.26	0.95	0.84	1.25	0.46
0.55	1.2	1.1	1.5	0.75
6.95	7.05	8.25	7.35	7.15
5.2	4.34	4.68	4.64	5.4
4.81	4.74	4.21	5.04	5.01
3.96	4.07	3.96	4.37	4.16
3.88	3.78	3.25	4.08	4.08
2.69	2.4	2.81	2.7	2.89
2.36	2.35	2.7	2.65	2.56
2.24	2.28	2.35	2.58	2.44
1.9	2.07	1.94	2.37	2.1
1.7	1.95	1.68	2.25	1.9
0.57	1.67	1.47	1.97	0.77
0.47	0.89	1.1	1.19	0.67
];

figure(1)
plot(Data,'linewidth',1.0)
grid
legend('C1','C2','C3','C4','C5')


x=0:15;
x=x';

c1=Data(:,1);
c2=Data(:,2);
c3=Data(:,3);
c4=Data(:,4);
c5=Data(:,5);



f1 = fit(x(5:16),c1(5:16),'exp1');
f2 = fit(x(5:16),c2(5:16),'exp1');
f3 = fit(x(5:16),c3(5:16),'exp1');
f4 = fit(x(5:16),c4(5:16),'exp1');
f5 = fit(x(5:16),c5(5:16),'exp1');


figure(2)
plot(f1,'b')
hold on
plot(f2,'r')
plot(f3,'g')
plot(f4,'m')
plot(f5,'k')
yline(1.5228, '--')
grid
axis([0 17 0 7.5])
legend('C1','C2','C3','C4','C5')

Thank you.

[Torsten]

f1(0),...,f5(0) are the y-intercepts.

[Sarfaraz Ahmed]

Thank you for your answer. Actually, this one for y-intercept. I want to get intercept with yline(1.5228, '--').

for example, in the attached figure intercept for "f1" is "12.492". however when I display f1 it shows y-intercept not y-line intercept. can you please let me know how can I get intercept with y-lines ? I corrected a question little bit as well.

Thank you

Answer 1

[Torsten]

a = f1.a;
b = f1.b;
xintercept1 = 1/b*log(1.5228/a);

(Same for f2,f3,f4 and f5)

[Sarfaraz Ahmed]

Great. It helps .

Thank you so much !!

Answer 2

[DGM]

Consider the example:

Data=[
    0.11	0.3	0.28	0.6	0.31
    0.23	0.78	0.57	1.08	0.43
    0.26	0.95	0.84	1.25	0.46
    0.55	1.2	1.1	1.5	0.75
    6.95	7.05	8.25	7.35	7.15
    5.2	        4.34    4.68	4.64	5.4
    4.81	4.74	4.21	5.04	5.01
    3.96	4.07	3.96	4.37	4.16
    3.88	3.78	3.25	4.08	4.08
    2.69	2.4	2.81	2.7	2.89
    2.36	2.35	2.7	2.65	2.56
    2.24	2.28	2.35	2.58	2.44
    1.9	        2.07	1.94	2.37	2.1
    1.7	        1.95	1.68	2.25	1.9
    0.57	1.67	1.47	1.97	0.77
    0.47	0.89	1.1	1.19	0.67
    ];

ymark = 1.5228; % need to be able to use this

x = (0:15).';

plotcolors = {'b','r','g','m','k'};

f = cell(size(Data,2),1);
fk = zeros(size(Data,2),2);
for kn = 1:numel(f)
    f{kn} = fit(x(5:16),Data(5:16,kn),'exp1');
    fk(kn,:) = coeffvalues(f{kn});
    plot(f{kn},plotcolors{kn})
    hold on
end
yline(ymark, '--');

grid
axis([0 17 0 7.5])

intx = log(ymark./fk(:,1))./fk(:,2); % inverse of fit function
plot(intx,ymark,'kx') % show with marker

legend('C1','C2','C3','C4','C5')