Solving differential equations with MATLAB syms a,b,c,d; dsolve('Dy(1)=1/2*a*y(2)*j','Dy(2)=-(c+d)*y(2)*j+1/2*a*y(1)*j+1/2*b*y(3)*j','Dy(3)=-d*y(3)*j+1/2*b*y(2)*j') error(' symbolic:dsolve :errmsg2','There are more ODEs than variables.') Why wrong? Where's the problem,

Solving differential equations with MATLAB syms a,b,c,d; dsolve('Dy(1)=1/2*a*y(2)*j','Dy(2)=-(c+d)*y(2)*j+1/2*a*y(1)*j+1/2*b*y(3)*j','Dy(3)=-d*y(3)*j+1/2*b*y(2)*j') error(' symbolic:dsolve :errmsg2','There are more ODEs than variables.') Why wrong? Where's the problem,

syms a,b,c,d； （x）
clc;clear all;
syms a b c d;
dsolve('Dy(1)=1/2*a*y(2)*j','Dy(2)=-(c+d)*y(2)*j+1/2*a*y(1)*j+1/2*b*y(3)*j','Dy(3)=-d*y(3)*j+1/2*b*y(2)*j')
error(' symbolic:dsolve :errmsg2','There are more ODEs than variables.')

Write out the matlab program of drawing the square of function y = x + X-1 image
Thank you for your brief reply

ezplot('y=x^2+x-1')

How to draw the function image of F (x) = (x | 1-x ^ 2 |) / (x ^ 2-1)
Tell me the method or pay attention to it. It's better to be more detailed

The key depends on the positive and negative of x ^ 2-1
X ^ 2-1 > 0 f (x) = x x ∈ (negative infinity, - 1) U (1, positive infinity)
x^2-1

Matlab draw piecewise function x > = 1, y = exp (- (x-1) ^ 2), X

x=-4:0.1:4;
y=(x=1).*(exp(-(x-1).^2));
plot(x,y,'--g')
text(-2,5,'\leftarrow y=x^2','FontSize',9)
text(2,0.7,'\leftarrow y=exp(-(x-1)^2)','FontSize',9)