===== Primitive: Soft object [Wyvill et al. 1986] =====

**Definition**: <m>f(r)= 1 - 22*r^2/{9*d^2} + 17*r^4/{9*d^4} - 4*r^6/{9*d^6}</m>
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r - distance to the given point

**Call**: hfSoft(x,x0,y0,z0,d,T);

**Parameters**:

x - point coordinates

x0,y0,z0 - arrays of blob centers

d - array of d - radii of influence

T - threshold value

**Test file**: [[http://hyperfun.org/soft.hf|soft.hf]]