FeynCalc manual (development version)

Coefficient2

Coefficient2[exp, form1, form2, ...] is like Coefficient, but it also allows to extracts coefficients of form1, form2, ... sequentially. To specify the power in formi, write it as {var,pow}.

To keep the prefactor whose coefficient you extracted you need to set the option Prefactor to True.

See also

Overview, Cases2.

Examples

ex = y0 + ep y1 + a4 (1/ep x1 + x2 + x3 ep) + a4^2 (1/ep^2 z1 + 1/ep z2 + z3 + x4 ep)

a42(z1ep2+ep  x4+z2ep+z3)+a4(x1ep+ep  x3+x2)+ep  y1+y0\text{a4}^2 \left(\frac{\text{z1}}{\text{ep}^2}+\text{ep} \;\text{x4}+\frac{\text{z2}}{\text{ep}}+\text{z3}\right)+\text{a4} \left(\frac{\text{x1}}{\text{ep}}+\text{ep} \;\text{x3}+\text{x2}\right)+\text{ep} \;\text{y1}+\text{y0}

Coefficient2[ex, a4]

x1ep+ep  x3+x2\frac{\text{x1}}{\text{ep}}+\text{ep} \;\text{x3}+\text{x2}

Coefficient2[ex, a4, 2]

z1ep2+ep  x4+z2ep+z3\frac{\text{z1}}{\text{ep}^2}+\text{ep} \;\text{x4}+\frac{\text{z2}}{\text{ep}}+\text{z3}

Coefficient2[ex, {a4, 2}]

z1ep2+ep  x4+z2ep+z3\frac{\text{z1}}{\text{ep}^2}+\text{ep} \;\text{x4}+\frac{\text{z2}}{\text{ep}}+\text{z3}

Coefficient2[ex, {a4, 2}, {ep, -1}]

z2\text{z2}

Coefficient2[ex, {a4, 2}, ep]

x4\text{x4}

Coefficient2[ex, a4, 2, ep]

x4\text{x4}

Coefficient2[ex, {a4, 1}, {ep, 0}]

x2\text{x2}

Coefficient2[ex, a4, ep]

x3\text{x3}

Coefficient2[ex, {a4, 1}, {ep, 0}, Prefactor -> True]

a4  x2\text{a4} \;\text{x2}