MATLAB: Selecting positive or negative terms of a symbolic vector

symbolic

I have a symbolic vector say [a^2*b^3, 0, -a*b^2, b^2, -a^4*b]. I would like to obtain two vectors from this. One of them only selecting the entries that have a positive coefficient, in this case I would like to obtain [a^2*b^3, b^2]. The other containing the entries with negative coefficient: [-a*b^2, -a^4*b].

I tried extracting the coefficients and then using if statement to create a vector with the positive entries and similar for the negative.

Is there a more efficient way to do this?

Best Answer

This works:

syms a b c 
V =  [a^2*b^3, 0, -a*b^2, b^2, -a^4*b];
Vs = sign(V);
Vgz = V(Vs>0)
Vlz = V(Vs<0)
Vgz =
[ a^2*b^3, b^2]
Vlz =
[ -a*b^2, -a^4*b]

Related Solutions

MATLAB: Conversion to logical from sym is not possible. I want the first argument to be a logical argument which has && for non symbolic variables, In a piecewise function.

You may try this code assuming it still satisfies your requirements.

syms a b c1 x;
assume(a==10);
assume(b==4);
assume(c1==2);
mu1 = 1;
sig1 = 0.5;
pdf1(x) = piecewise( a == 0 & b < 0 , -(1/(b*exp((c1 - x + b*mu1)^2/(2*b^2*sig1^2))*sqrt(2*pi)*sig1)),...
           a == 0 & b > 0, 1/(b*exp((c1 - x + b*mu1)^2/(2*b^2*sig1^2))*sqrt(2*pi)*sig1),...
a ~= 0 & (-b^2 + 4*a*c1 - 4*a*x) < 0,(exp((b - sqrt(b^2 - 4*a*c1 + 4*a*x) + 2*a*mu1)^2/(8*a^2*sig1^2)) + exp((b + sqrt(b^2 - 4*a*c1 + 4*a*x) + 2*a*mu1)^2/(8*a^2*sig1^2)))/(exp((b^2 + 2*a*b*mu1 + 2*a*(-c1 + x + a*mu1^2))/(2*a^2*sig1^2))*sqrt(2*pi)*sqrt(b^2 + 4*a*(-c1 + x))*sig1),...
 0);

syms a b c1 x;
mu1 = 1;
sig1 = 0.5;
pdf1(a,b,c1,x) = piecewise( a == 0 & b < 0 , -(1/(b*exp((c1 - x + b*mu1)^2/(2*b^2*sig1^2))*sqrt(2*pi)*sig1)),...
           a == 0 & b > 0, 1/(b*exp((c1 - x + b*mu1)^2/(2*b^2*sig1^2))*sqrt(2*pi)*sig1),...
a ~= 0 & (-b^2 + 4*a*c1 - 4*a*x) < 0,(exp((b - sqrt(b^2 - 4*a*c1 + 4*a*x) + 2*a*mu1)^2/(8*a^2*sig1^2)) + exp((b + sqrt(b^2 - 4*a*c1 + 4*a*x) + 2*a*mu1)^2/(8*a^2*sig1^2)))/(exp((b^2 + 2*a*b*mu1 + 2*a*(-c1 + x + a*mu1^2))/(2*a^2*sig1^2))*sqrt(2*pi)*sqrt(b^2 + 4*a*(-c1 + x))*sig1),...
 0);

MATLAB: Selecting non-zero elements from a symbolic vector

This works for me (in R2015a):

syms a b c 
V = [a*b, 0 , a^2*b*c, 1, 0];
Vnz = V(V~=0)
Vnz =
[ a*b, a^2*b*c, 1]

Best Answer

Related Solutions

MATLAB: Conversion to logical from sym is not possible. I want the first argument to be a logical argument which has && for non symbolic variables, In a piecewise function.

MATLAB: Selecting non-zero elements from a symbolic vector

Related Question