Importing 3 spectrum data, plot representative spectrum for each sample all in same figure

I have spectrum data from three different samples. I am supposed to import the wavelength and absorbance spectra data from each file, make a reresentative spectrum from each sample, and plot in the same figure. Please help. Here is the code for two of my files.

clear

test=imread('curc_1.jpeg');

test2=rgb2gray(im2double(test));

image(test);

test_spectrum=sum(test2(1750:2500,1800:3000),1);

figure();plot(test_spectrum);

m=0.406;b=336.64;L=b+m*(0:1:numel(test_spectrum)-1);

plot(L,test_spectrum);

for i=1:4

test=imread(['curc_',num2str(0+i),'.jpeg'])

test2=rgb2gray(im2double(test));

spectra(i,:)=sum(test2(1750:2500,1800:3000),1);

end

plot(L,spectra)

for i=2:4;absorbance(i-1,:)=-1*log10(spectra(i,:)./spectra(1,:));end

plot(L,absorbance)

set(gca,'fontsize',14);xlabel('wavelength(nm)');ylabel('absorbance(a.u)')

clear

test=imread('carrot_1.jpeg');

test2=rgb2gray(im2double(test));

image(test);

test_spectrum=sum(test2(1750:2500,1800:3000),1);

figure();plot(test_spectrum);

m=0.406;b=336.64;L=b+m*(0:1:numel(test_spectrum)-1);

plot(L,test_spectrum);

for i=1:4

test=imread(['curc_',num2str(0+i),'.jpeg'])

test2=rgb2gray(im2double(test));

spectra(i,:)=sum(test2(1750:2500,1800:3000),1);

end

plot(L,spectra)

for i=2:4;absorbance(i-1,:)=-1*log10(spectra(i,:)./spectra(1,:));end

plot(L,absorbance)

set(gca,'fontsize',14);xlabel('wavelength(nm)');ylabel('absorbance(a.u)')

Answer 1

[Julius Muschaweck]

It's hard to reproduce what you did without the jpeg files.

But, maybe hold on is what you need:

figure();
plot([1 2],[1 2]);
hold on;
plot([1 2],[2 1]);

gives you