intrgartion_problem..

Hi im trying to run a code i call in some point the folllow lines

y_theory=@(t)((1./(P.*Zl)).*f_xi(t./(Zl*P)))./(g_norm);

x=0:1e-6:V2L;

yi=@(x)integral(y_theory,0,x,'ArrayValued',true)

plot(x,yi(x),'r','LineWidth',2)
xlabel('|V_{L}|(V)')
ylabel('f(|V_{L}|)(1/v)')

and i recieve the message

Error using integral (line 86)
A and B must be floating point scalars.

Error in @(x)integral(y_theory,0,x,'ArrayValued',true)
Error in main_distr_polarization4VL_cum (line 160)
plot(x,yi(x),'r','LineWidth',2)

what is the problem?

thank you in advance George

Answer 1

[John D'Errico]

integral does not have the capability to solve a problem with multiple limits of integration. The help never states that the limits of integration can be anything other than a scalar value.

The arrayvalued flag is not designed to solve arrays of limits, but array valued functions! There is a big difference. From the help for integral:

'ArrayValued', FUN is an array-valued function when the input is scalar

That you want it to work in away that it is not designed to work is not relevant. Of course, nothing stops you from using a loop to accomplish this task. You can even make it efficient. Thus...

Since x is the upper limit of integration, and x varies as

x=0:1e-6:V2L;

then use integral to compute the integral between each increment in x, then use cumsum to compute the cumulative integral. This avoids forcing integral to compute the integral of the same region multiple times.

Sometimes a loop is the simplest solution. But assuming that code will somehow magically know what it is that you wanted to do is rarely the correct approach.

[george veropoulos]

thank you

you mean that

xi=0:1e-6:V2L;

yi=((1./(P.*Zl)).*f_xi(xi./(Zl*P)))./(g_norm);
cdf_theory=cumsum(yi)

[Walter Roberson]

y_theory=@(t)((1./(P.*Zl)).*f_xi(t./(Zl*P)))./(g_norm);

x=0:1e-6:V2L;

yi_parts = arrayfun( @(idx) integral(y_theory, x(idx), x(idx+1)), 1:length(x)-1 );
yi = cumsum( yi_parts );

[John D'Errico]

Walter has it right. Though it could be done using a loop too.