how to get Y Value from a plot having 3 curves as shown in figure?

Hi all,

Please give me method to solve this problem either in script or App Designer any method is lot of helpful.

Question Described : I have a plot with multiple curve (Image attached).

Input i have X axis and Curve Data, for this i need to get Y value.

Plot looks like this. see Attachment >> Now For X value (@ point Q between P1 & P2) I should find Y.

Here If i give 2 inputs

Input1 >> data of P1,P2 Or P3 Or inbetween P1 & P2

input2>> X value

Output Requried Y >> for above inputs.

Thanks for Help.

Answer 1

[Star Strider]

Try something like this —

x = linspace(0, 5);
C1 = 5+(x-2).^2;
C2 = 2+(x-1).^4;

xint = interp1(C1-C2, x, 0)

xint = 2.3275

yint = interp1(x, C1, xint)

yint = 5.1074

figure
hp1 = plot(x, C1);
hold on
hp2 = plot(x, C2);
plot([0 xint], [1 1]*yint, '--k')
plot([1 1]*xint, [0 yint], '--k')
hp3 = plot(xint, yint, 'xg', 'MarkerSize',15);
hold off
grid
legend([hp1,hp2,hp3], 'C_1', 'C_2', 'Intersection', 'Location','best')
ylim([0,15])

I have no idea if your curves are functions or data. If they are functions, it would be necessary to evaluate them first to use this code. (If they are functions and you want to evaluate the intersections as functions, you would need to use fzero or fsolve.)

.

[naveen kumar s]

my curves are just data values.

I will Try this code too, Thank you lot

&

The Above figure showing intersection of C1 & C2 for that Y value is approx. 5.

Now if i want to get value of Y for C1 only @ X = 4. --> For this above same code works?

@Star Strider Thank You

[Star Strider]

‘Now if i want to get value of Y for C1 only @ X = 4. --> For this above same code works?’

Yes.

For any value for either ‘x’ or ‘y’ that the curves intersect, you can use my code to find the other value.

Example —

x = linspace(0, 5);
C(1,:) = 5+(x-2).^2;
C(2,:) = 2+(x-1).^4;

xq = 1.3;                                                   % Find 'y' Values For This 'x'

for k = 1:size(C,1)
    yi(k) = interp1(x,C(k,:),xq);
end
yi

yi = 1×2

5.4905 2.0084

yq = 7.25;                                                  % Find 'x' Values For This 'y'

for k1 = 1:size(C,1)
    [~,idx] = min(C(k1,:));
    idxrng{k1} = {[1:idx]; [idx+1:numel(C(k1,:))]};
    for k2 = 1:2
        idxv = idxrng{k1}{k2};
        xq = interp1(C(k1,idxv), x(idxv), yq);
        xi(k1,k2) = xq;
    end
end
xi

xi = 2×2

0.5001 3.4998 NaN 2.5132

I did not plot these this time, however that is straightforward to do. Since NaN values do not plot, they will not appear on the plot. The intent is to show that the code is robust to returning values for values that are not on the curves.

.

[naveen kumar s]

Yes, I have understood your code. Thank you again.

One more Question i would like to add.

If xq = 1.3 finding >>this is my 1st input %for finding Y calue at that x.

Again

If I give my 2nd input inbetween C1 & C2 : say from my question between P1 & P2 @point Q (value like 14 - inbetween P1 = 10, P2 = 20)

for this 2 input. Only One Value of Y can i get.

Example >>

xq = 1.3;

C = 5;

output >>

Yi = (may be arround 4 from your chart of C1 & C2)

Thank you

[Star Strider]

As always, my pleasure!

I need more information.

My code only returns points on the curves, so ‘Point Q’ is not defined, and can be anything. If ‘Q’ is defined on a surface defined by ‘P1’, ‘P2’, and ‘P3’ (and a third ‘z’ value for each curve), it is certainly possible to define it using the scatteredInterpolant function.

There are of course other possibilities, however it will be necessary to know more about how the curves are related in order to determine the value of ‘Q’. Is there any sort of functional relationship between the curves? Is there any way to interpolate between them?

At present, there is simply not enough information to write specific code.

For the curves in my example, to get a specific ‘y’ value between the values of ‘yi’, it would be necessary to know how the curves are related (since in my code they are simply random and have no functional relationship, such as a ‘z’ value, or being calculated from a function such that the two curves are the result of using different parameters in the same function).

.

[naveen kumar s]

@Star Strider Really appreciate your valuable time.

Yes I have to use Scattered interpolant.

I tried but still its not working i knew i made somewhere mistake findind it. (even i will attach code also)

I have attached plot from matlab after running code.

@ inputs Xq @ different P. >> i got output but it is taking at X axis but not taking P.

alldata = load ('MPpsy.mat');

save('MPpsy.mat','-struct','alldata');

r = 50;

% curves of P5 to Pn x & y values are not in same size.

X1 = (linspace(alldata.p5(1,1), alldata.p5(end,1),r))';

Y1 = interp1(alldata.p5(:,1),alldata.p5(:,2),X1,'linear');

X2 = (linspace(alldata.p6(1,1), alldata.p6(end,1),r))';

Y2 = interp1(alldata.p6(:,1),alldata.p6(:,2),X2,'linear');

X3 = (linspace(alldata.p7(1,1), alldata.p7(end,1),r))';

Y3 = interp1(alldata.p7(:,1),alldata.p7(:,2),X3,'linear');

X4 = (linspace(alldata.p8(1,1), alldata.p8(end,1),r))';

Y4 = interp1(alldata.p8(:,1),alldata.p8(:,2),X4,'linear');

X5 = (linspace(alldata.p9(1,1), alldata.p9(end,1),r))';

Y5 = interp1(alldata.p9(:,1),alldata.p9(:,2),X5,'linear');

X6 = (linspace(alldata.p10(1,1), alldata.p10(end,1),r))';

Y6 = interp1(alldata.p10(:,1),alldata.p10(:,2),X6,'linear');

X7 = (linspace(alldata.p12(1,1), alldata.p12(end,1),r))';

Y7 = interp1(alldata.p12(:,1),alldata.p12(:,2),X7,'linear');

X8 = (linspace(alldata.p14(1,1), alldata.p14(end,1),r))';

Y8 = interp1(alldata.p14(:,1),alldata.p14(:,2),X8,'linear');

X9 = (linspace(alldata.p16(1,1), alldata.p16(end,1),r))';

Y9 = interp1(alldata.p16(:,1),alldata.p16(:,2),X9,'linear');

X10 = (linspace(alldata.p18(1,1), alldata.p18(end,1),r))';

Y10 = interp1(alldata.p18(:,1),alldata.p18(:,2),X10,'linear');

X11 = (linspace(alldata.p20(1,1), alldata.p20(end,1),r))';

Y11 = interp1(alldata.p20(:,1),alldata.p20(:,2),X11,'linear');

X12 = (linspace(alldata.p25(1,1), alldata.p25(end,1),r))';

Y12 = interp1(alldata.p25(:,1),alldata.p25(:,2),X12,'linear');

X13 = (linspace(alldata.p30(1,1), alldata.p30(end,1),r))';

Y13 = interp1(alldata.p30(:,1),alldata.p30(:,2),X13,'linear');

X14 = (linspace(alldata.p35(1,1), alldata.p35(end,1),r))';

Y14 = interp1(alldata.p35(:,1),alldata.p35(:,2),X14,'linear');

X15 = (linspace(alldata.p40(1,1), alldata.p40(end,1),r))';

Y15 = interp1(alldata.p40(:,1),alldata.p40(:,2),X15,'linear');

X16 = (linspace(alldata.p50(1,1), alldata.p50(end,1),r))';

Y16 = interp1(alldata.p50(:,1),alldata.p50(:,2),X16,'linear');

X17 = (linspace(alldata.p60(1,1), alldata.p60(end,1),r))';

Y17 = interp1(alldata.p60(:,1),alldata.p60(:,2),X17,'linear');

X18 = (linspace(alldata.p70(1,1), alldata.p70(end,1),r))';

Y18 = interp1(alldata.p70(:,1),alldata.p70(:,2),X18,'linear');

X19 = (linspace(alldata.p80(1,1), alldata.p80(end,1),r))';

Y19 = interp1(alldata.p80(:,1),alldata.p80(:,2),X19,'linear');

X20 = (linspace(alldata.p90(1,1), alldata.p90(end,1),r))';

Y20 = interp1(alldata.p90(:,1),alldata.p90(:,2),X20,'linear');

X21 = (linspace(alldata.p100(1,1), alldata.p100(end,1),r))';

Y21 = interp1(alldata.p100(:,1),alldata.p100(:,2),X21,'linear');

X22 = (linspace(alldata.p120(1,1), alldata.p120(end,1),r))';

Y22 = interp1(alldata.p120(:,1),alldata.p120(:,2),X22,'linear');

X23 = (linspace(alldata.p150(1,1), alldata.p150(end,1),r))';

Y23 = interp1(alldata.p150(:,1),alldata.p150(:,2),X23,'linear');

X24 = (linspace(alldata.p200(1,1), alldata.p200(end,1),r))';

Y24 = interp1(alldata.p200(:,1),alldata.p200(:,2),X24,'linear');

X25 = (linspace(alldata.p250(1,1), alldata.p250(end,1),r))';

Y25 = interp1(alldata.p250(:,1),alldata.p250(:,2),X25,'linear');

X26 = (linspace(alldata.p300(1,1), alldata.p300(end,1),r))';

Y26 = interp1(alldata.p300(:,1),alldata.p300(:,2),X26,'linear');

xx = [X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14 X15 X16 X17 X18 X19 X20 X21 X22 X23 X24 X25 X26];

yy = [Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10 Y11 Y12 Y13 Y14 Y15 Y16 Y17 Y18 Y19 Y20 Y21 Y22 Y23 Y24 Y25 Y26];

zz =linspace(5,300,50);

% zz = [5 6 7 8 9 10 12 14 16 18 20 25 30 35 40 50 60 70 80 90 100 120 150 200 250 300];% Trail check

X_axes= input('X = ');

P_curves= input('P = ');

P_x = interp1(zz,xx,P_curves,'linear','extrap');

P_y = interp1(zz,yy,P_curves,'linear','extrap');

Y = interp1(P_x,P_y,X_axes,'linear','extrap')

plot(xx,yy)

axis([-50 100 0 0.034])

hold on

plot(X_axes,humidity,'*')

here is code .

New Question :

Here i used my mat file saved as struct. ( for all P curves, X &Y are in different size : So X1 Y1 to X26 Y26 did interpolation to maintain size. >> Can I Do This Using FOR function Less Steps.

&

Yes finally what mistake in my code why I am not getting Y exactly.

[Star Strider]

That is very difficult for me to follow.

Also, there is no plot.

With respect to using a for loop, that is definitely a possibility. However, it would be necessary to use struct2cell or struct2table (if possible) to extract the structure to some sort of array, since structures themselves would be difficult (or impossible) to index in a loop (at least for me, since I have never tried it).

.

Answer 2

[KALYAN ACHARJYA]

I have assumed that you have the 3 data for three individual plot, with respect to same x values, let say y1,y2,y3 for the same value of x

val1=abs(y1-y2)
idx=find(val1==min(val1))  %Get the index of first intersection of y1 & y2 
x_id1=x_data(idx);

Do the same for other plot, also you may look for other solutions too-

https://in.mathworks.com/matlabcentral/answers/435138-find-intersection-of-graph

https://in.mathworks.com/matlabcentral/answers/105201-how-do-you-find-the-intersection-points-of-two-functions

[naveen kumar s]

thank you so much. I will try this give you me feedback.

[naveen kumar s]

Actually,

The plot Above Shown is just Example ;

In my Plot there is no Intersection of all curves.

Plot looks like this. see Attachment >> Now For X value (@ point Q between P1 & P2) I should find Y.

Here If i give 2 inputs

Input1 >> P1,P2 Or P3 Or inbetween P1 & P2

input2>> X value

Output Requried Y >> for above inputs.

@KALYAN ACHARJYA This is my actual Question. I will update above also.

Thanks for your help.