range in symbolic form

I have this problem:

solution=feval(symengine, 'solve', '(abs(8/(k1+1)))<1', 'k1', 'Real') 

solution = (7, Inf) union (-Inf, -9)

The solution is symbolic, but I need to have the two range in numeric form (array?) inside a script. Do I have to write about ten lines of code to do it? Thank you

Answer 1

[riccardo agnesi]

for my system I solved it this way alone.

I wanted something like that:

            syms x
            P = expand((x-3/2)*(x-5/4)*(x-1/10)*(x+4/8)*(x-12/5))
            [ cond, condCell ] = inequality( P, 'x', 'P>0' )

The result, in symbolic form is: (-1/2, 1/10) union (5/4, 3/2) union (12/5, Inf). With my function, I have the result in numeric form (cond) and symbolic form, but separated into minimum and maximum.

cond =

-0.5000 0.1000

1.2500 1.5000

2.4000 Inf

condCell =

'-1/2' ' 1/10'

'5/4' ' 3/2'

'12/5' ' Inf'

I'm curious if there is another solution for my conditions (operating system xp, computer 20 years old, matlab 2010a)

function [ ra, racell ] = inequality( P, var, test )

    test = subs(test,P);
    s = feval(symengine, 'solve', test, var, 'Real')

    if(isempty(s))                  %no solution
        ra=[1 -1];                  %lower > higher
        racell = {'no solution' ''};
    else
        s = char(s);
        r = strfind(s,'R_');

        if(isempty(r))
            u = strfind(s,'union');
            j = strfind(s,'Interval');

            [r,c]=size(j);

        %L=[0 0 0];
        %racell = cell(1,2);

            for(i=1:c)
                if(i<c)
                    II = s(j(i)+9 : u(i)-3);
                else
                    II = s(j(i)+9 : end -1);
                end
    
                kv = strfind(II,',');

                v1 = II(1:kv-1);
                v2 = II(kv+1:end);
    
                try
                    L(i,:) = [sym2poly(vpa(v1)) sym2poly(vpa(v2)) i];
                catch exception
                    L(i,:) = [(vpa(v1)) (vpa(v2)) i];
                end
    
                SS(i,1) = cellstr(v1);
                SS(i,2) = cellstr(v2);
            end

            L = sortrows(L,1);

            for(i=1:c)
                ind = (L(i,3));
                racell(i,1)=SS(ind,1);
                racell(i,2)=SS(ind,2);
            end
            ra=L(:,1:2);

            [ra racell] = checkrange(ra, racell);
        else
            ra = [-Inf Inf];
            racell = {'-Inf' 'Inf'};
        end
    end
end

function [ra racell] = checkrange(rain, racellin)

    [r,c] = size(rain);
    
    j=1;
    ra(j,1) = rain(1,1);
    ra(j,2) = rain(1,2);
    
    racell(j,1)=racellin(1,1);
    racell(j,2)=racellin(1,2);
    
    for i=2:r
        
        if(rain(i,1) == rain(i-1,2))
            
            ra(j,2) = rain(i,2);
            racell(j,2)=racellin(i,2);
        else
            j = j + 1;
            
            ra(j,1) = rain(i,1);
            ra(j,2) = rain(i,2);
            
            racell(j,1)=racellin(i,1);
            racell(j,2)=racellin(i,2);
        end
    end
end

Answer 2

[Walter Roberson]

ch = children(solution);
[children(ch(1)),children(ch(2))]

[riccardo agnesi]

ch = children(solution);

[children(ch(1)),children(ch(2))]

??? Undefined function or method 'children' for input arguments of type 'sym'.

[Walter Roberson]

You might have a corrupt MATLAB installation.

... Or you might have forgotten to mention that you are using a version before R2012a, which would be important information in order to know how to solve the difficulty.

[riccardo agnesi]

Ops. I'm using a 20-year-old pc with the xp operating system and matlab 2010a

[Walter Roberson]

I don't think I have a virtual machine for a MATLAB that old...