sum y-values where they do overlap of different x- and y-vectors

What kind of different ways are available to sum up the y-values where the different y-values do overlap each other (see plot(x1,y1,x2,y2)). The problem is here that the x-vectors doesn't have the same starting point. This example script below is a simplified script of the file with 24 different x-vectors (see further below).

%%simplified example
x1 = 250:260;
y1 = [0 0.2 0.3 0.5 0.55 0.6 0.55 0.5 0.3 0.2 0 ];
x2 = 255:265;
y2 = y1*0.8;
figure; plot(x1,y1,x2,y2)

%%script with 24 different x-vectors
sigma = 1;
step=0.01;
min = -10;
max = 10;

%%v',v'' =      0,4 -       0,5 -       1,4 -       3,13
FCF_A3_X1 = [   .1408e-0    .1854e-0    .1106e-0    .1170e-0 ];
x0_A3_X1 = [    246.3       260.5       237.9       385.7 ];
%%v',v''_ =    0,0 -       0,1 -       1,5 -       2,1 -       2,6 -       2,7 -       3,1 -       3,6 -       4,7
FCF_C3_B3 = [   .4527e-0    .3291e-0    .4663e-1    .3413e-0    .7913e-1    .3622e-1    .2536e-0    .1292e-0    .1000e-0];
x0_C3_B3 = [    337.0       357.6       426.8       313.5       420.0       448.9       296.1       389.4       385.6];
%%v',v'' =     2,0 -       3,0 -       5,0 -       5,1 -       6,3 -       7,5 -       8,6 -       9,5 -       9,6 -       10,6 -      12,7
FCF_B3_A3 = [   .1617e-0    .3423e-1    .2680e-3    .1640e-1    .2311e-0    .7415e-1    .1991e-1    .1564e-0    .2493e-0    .1990e-0    .7324e-1];
x0_B3_A3 = [    773.2       685.8       562.2       611.4       660.8       714.7       704.2       589.4       638.0       584.3       536.3];

figure
for i=1:length(x0_A3_X1);
  x_A3_X1(i,:) = x0_A3_X1(i)+min :step: x0_A3_X1(i)+max;
  f_A3_X1(i,:) = exp(-(x_A3_X1(i,:)-x0_A3_X1(i)).^2./(2*sigma^2));
  f_cor1(i,:) = f_A3_X1(i,:)*FCF_A3_X1(i);

    for j=1:length(x0_C3_B3);
        x_C3_B3(j,:) = x0_C3_B3(j)+min :step: x0_C3_B3(j)+max;
        f_C3_B3(j,:) = exp(-(x_C3_B3(j,:)-x0_C3_B3(j)).^2./(2*sigma^2));
        f_cor2(j,:) = f_C3_B3(j,:)*FCF_C3_B3(j);

        for k=1:length(x0_B3_A3);
            x_B3_A3(k,:) = x0_B3_A3(k)+min :step: x0_B3_A3(k)+max;
            f_B3_A3(k,:) = exp(-(x_B3_A3(k,:)-x0_B3_A3(k)).^2./(2*sigma^2));
            f_cor3(k,:) = f_B3_A3(k,:)*FCF_B3_A3(k);

                plot(x_A3_X1(i,:),f_cor1(i,:),x_C3_B3(j,:),f_cor2(j,:),x_B3_A3(k,:),f_cor3(k,:));
            hold on
            %pause(0.2)

        end
    end
end

[Richa Gupta]

Can you explain how is x-vectors not having the same starting point related to summing up the y-values?