"solve" bug?

Hello everyone, I am writing because I have a problem with the resolution of inequality.

syms x;
f = 6*x + 24;
s = solve(f < 0, x, 'Real', true)

This is the result:

s =

-5

I have tried everything to fix it. Because the result is wrong? Correct result: x <- 4. Sorry for my bad English

[Star Strider]

Just using:

s = solve(f)

gives -4 as expected.

[Robert Leo]

But I want the interval

Answer 1

[MHN]

It gives you the first integer number that meets the criteria (f<0) which is -5 (for -4 you should write f<=0). Matlab is not a good tool for symbolic calculation and I do not think it gives you that result (x<-4, or x<=-5). Btw, of course it is not a bug in solve function !!!

[Robert Leo]

Ok, thanks for the answer. But how do I solve my problem? What can I use? With f <= 0 the result does not change

Answer 2

[Raghad Alharbi]

Selection = menu ('Welcome to Relations' ...

'Reflexivity' ...

'Symmetry' ...

'Transitivity' ...

'Exit the menu')

A = [0,1,2,3,4,5]; Z1 = []; Z2 = []; Z3 = [];

while Selection < 7

switch Selection

case 1 Reflexivity

i = 1;

while i < 7

n1 = input(' Enter rfist integer for n1; ');

if ismember ([n1],A) == 1

fprintf('n1 belongs to A\n')

break

else

i = i+1;

end

end

i = 1;

while i < 7

n2 = input('Enter rfist integer for n2; ');

if ismember ([n2],A) == 1

fprintf('n1 belongs to A\n')

break

else

i = i+1;

end

end

if ismember([n1],A) == 1 && ismember ([n2],A) == 1 && n1 == n2

fprintf('Yes, R Reflexivity\n')

else

fprintf('No, R is not Reflexivity\n')

end

case 2 Symmetry

n1 = input('Enter frist integer for n1: ');

n2 = input('Enter second integer for n2: ');

if ismember ([n1], A) == 1 && ismember ([n2] ,A) == 1 && n1 ~= n2

Z1 (end + 1) = n1;

Z1 (end + 1) = n2;

Z2 (end + 1) = n2;

Z2 (end + 1) = n1;

fprintf('Yes, R Symmetry\n')

else

fprintf('no, R is not Symmetry\n')

end

case 3 Transitivity

n1 = input('Enter frist integer for n1: ');

n2 = input('Enter second integer for n2: ');

n3 = input('Enter third integer for n3: ');

if ismember ([n1], A) == 1 && ismember ([n2] ,A) == 1 && ismember ([n3], A) == && n1 ~= n2 && n2 ~= n3

Z1 (end + 1) = n1;

Z1 (end + 1) = n2;

Z2 (end + 1) = n2;

Z2 (end + 1) = n3;

Z3 (end + 1) = n1;

Z3 (end + 1) = n3;

fprintf('Yes, R Transitivity\n')

else

fprintf('no, R is not Transitivity\n')

end

case 4 Exit menu

break;

end

Selection = menu('Welcome to Reflexivity, Symmetry, and Transitivity' ...

'Reflexivity' ...

'Symmetry' ...

'Transitivity' ...

'Exit the menu')

end

fprintf('You have left the menu, Have a good day!\n')