public String derive() {
String u, du, v, dv;
String value = token.getValue();
if (token.isVariable()) {
return one;
} else if (token.isNumber()) {
return zero;
} else if (value.equals(plus)) {
du = A.derive();
dv = B.derive();
return lB + du + value + dv + rB;
} else if (value.equals(minus)) {
du = A.derive();
dv = B.derive();
return lB + du + value + dv + rB;
} else if (value.equals(times)) {
u = A.getExpression();
du = A.derive();
v = B.getExpression();
dv = B.derive();
return lB + lB + u + value + dv + rB + "+" + lB + v + value + du + rB + rB;
} else if (value.equals(divide)) {
u = A.getExpression();
du = A.derive();
v = B.getExpression();
dv = B.derive();
return lB + lB + lB + v + "*" + du + rB + "-" + lB + u + "*" + dv + rB + rB + value + lB + v
+ "^2" + rB + rB;
} else if (value.equals(power)) {
// power is not a function of variable
u = A.getExpression();
du = A.derive();
v = B.getExpression();
return lB + v + "*" + u + value + lB + v + "-1" + rB + "*" + du + rB;
}
return "";
}
private String getExpression() {
if (A != null && B != null) {
return lB + A.getExpression() + token.getValue() + B.getExpression() + rB;
}
return token.getValue();
}