Pfthb

For the following MWE, I need to place block (yaw) C midway between (1) the middle point between (output) and (integrator) (2) and (sum2).

So, how can I correct this syntax node [block] (yaw) at ([yshift=-2cm]$(integrator)+0.5*(output)-(integrator)!0.5!(sum2)$) C; to make it work?

documentclassarticle
usepackagetikz,mathtools,amssymb
usetikzlibraryshapes,arrows,positioning,calc

begindocument

tikzset
block/.style = draw, fill=white, rectangle, minimum height=3em, minimum width=3em,
tmp/.style = coordinate, 
sum/.style= draw, fill=white, circle, node distance=1cm,
input/.style = coordinate,
output/.style= coordinate,
pinstyle/.style = pin edge=to-,thin,black



begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 node [block] (yaw) at ([yshift=-2cm]$(integrator)+0.5*(output)-(integrator)!0.5!(sum2)$) C;
 %
 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output);
 endtikzpicture

enddocument

Additionally, is it possible to create a new node using node [tmp, below = 2cm of ($(output)!0.5!(integrator)$) ] (tmp1) ; without creating auxiliary nodes/coordinates?

I don't know how complex expression can be understood by calc but instead of trying to understand how to write such expression, I think it's easier to use an auxiliar coordinate and solve the problem:

documentclassarticle
usepackagetikz,mathtools,amssymb
usetikzlibraryshapes,arrows,positioning,calc

begindocument

tikzset
block/.style = draw, fill=white, rectangle, minimum height=3em, minimum width=3em,
tmp/.style = coordinate, 
sum/.style= draw, fill=white, circle, node distance=1cm,
input/.style = coordinate,
output/.style= coordinate,
pinstyle/.style = pin edge=to-,thin,black



begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 coordinate (aux) at ($(integrator.east)!.5!(output)$);
 node [block] (yaw) at ([yshift=-2cm]$(aux)!0.5!(sum2)$) C;
 draw (aux) |- (yaw);
 draw (yaw)-|(sum2);
 %
 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output);
 endtikzpicture

enddocument

Your approach does not work because you try to use and where you should use ($ and $). You can definitely do that without auxiliary coordinates and actually even without calc.

documentclassarticle
usepackagetikz,mathtools,amssymb
usetikzlibraryshapes,arrows,positioning,calc

begindocument

tikzset
block/.style = draw, fill=white, rectangle, minimum height=3em, minimum width=3em,
tmp/.style = coordinate, 
sum/.style= draw, fill=white, circle, node distance=1cm,
input/.style = coordinate,
output/.style= coordinate,
pinstyle/.style = pin edge=to-,thin,black



begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 node [block] (yaw) at 
 ($(0,-2cm)+($(output)!0.5!(integrator)$)!0.5!(sum2)$) C;
 %
 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output)
 coordinate[midway] (aux);
 draw (aux) |- (yaw) -| (sum2);
endtikzpicture

bigskip

begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 node [block] (yaw) at 
 ([yshift=-2cm]barycentric cs:output=1,integrator=1,sum2=2) C;
 %
 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output)
 coordinate[midway] (aux);
 draw (aux) |- (yaw) -| (sum2);
endtikzpicture

enddocument

Here, to simplify the code, I'll replace (integrator) with (A), (output) with (B) and (sum2) with (C).
There is two things not right with
($ (A) + 0.5* (B)-(A) !0.5!(C) $).

• First, I don't think you can use , with the calc package, for the coordinate part. For me, it only works for with scalar. So ($ 2+2*(A) $) will compute, but not ($ 2*(A)+(B) $) (or am I wrong?)




• The second thing is that this formula doesn't seem to correspond to the point you want.
  I kind of get that you want to start from (A), "move" to the middle of [AB] and continue like that, but you mix relative (B-A) and absolute positioning (C).
  One right formula would have been ($  (A) + 0.5*(B)-(A) !0.5!(C) $).
  But because tikz can't do the computation, you'll have to give the expanded formula: ($ .25*(A) + .25*(B) + .5*(C)$).

One other way to do it is ($ (A) !.5! (B) !.5! (C) $). Here, we take the middle of (A) and (B), and then the middle of the result and (C).

I hope this will answer your interrogations!

You can test the three solutions here (the last one with temporary coordinate):

documentclass[tikz,margin=10pt]standalone
usetikzlibrarycalc

begindocument

begintikzpicture[line width=1]

 draw[black!10] (0,0) grid (4,4);
 node (A) at (1,1) A;
 node (B) at (3,1) B;
 node (C) at (2,3) C;

 %% 1
 draw[red] ($ (A) !.5! (B) !.5! (C) $) circle (.05);
 %% 2
 draw[orange] ($ .25*(A) + .25*(B) + .5*(C) $) circle (.1);
 %% 3
 coordinate (foo) at ($ (A) !.5! (B) $);
 draw[yellow] ($ (foo) !.5! (C) $) circle (.15);

endtikzpicture
enddocument

which gives

The calc library allows you to apply Parway Modifiers repeatedly. Thus, the following syntax

($(integrator)!.5!!(output)!0.5!(sum2)$) 

does the following:

• pgf calculates the middle of (integrator) and (output)
  


• then calculates the middle of this last calculated point and the next one (sum2)
  

We can continue like this as many times as we want.

Here is for example page 144 of the manual 3.0.1a modified by adding two more points.

documentclassarticle
usepackagetikz
usetikzlibrarycalc

begindocument 
begintikzpicture[every node/.style=draw,circle,inner sep=1pt]
draw [help lines] (0,0) grid (3,2);
%first node
draw[densely dotted] (0,0) -- (3,2);
node at ($(0,0)!.3!(3,2)$) 1;
%second node
draw[densely dotted] ($(0,0)!.3!(3,2)$) -- (3,0);
node at ($(0,0)!.3!(3,2)!.7!(3,0)$)2;

%third node
draw[densely dotted] ($(0,0)!.3!(3,2)!.7!(3,0)$)--(3,2);
nodeat ($(0,0)!.3!(3,2)!.7!(3,0)!.6!(3,2)$) 3;

%fourth node
draw[densely dotted] ($(0,0)!.3!(3,2)!.7!(3,0)!.6!(3,2)$)--(0,2);
nodeat ($(0,0)!.3!(3,2)!.7!(3,0)!.6!(3,2)!.5!(0,2)$) 4;
endtikzpicture

enddocument

Unfortunately, this does not simplify the writing of the code. The use of an auxiliary point as @Ignasi did is therefore more elegant.

Updated just for fun: A complete solution with the calc library

And without using yshift=-2cm and without intermediate point (It's really complicated and unreadable!)

draw (sum2)|-($(integrator)!.5!(output)!0.5!(sum2)!2cm!90:(sum2)$)node[block]C-|($(integrator)!.5!(output)$);

But which places the point in the same place with the syntax indicated in the manual 3.0.1a p143, i quote:

The general meaning of <a>!<factor>!<angle>:<b> is “First, consider
the line from <a> to <b>. Then rotate this line by <angle> around the
point <a>.

documentclassarticle
usepackagetikz,mathtools,amssymb
usetikzlibraryshapes,arrows,positioning,calc

begindocument

tikzset
block/.style = draw, fill=white, rectangle, minimum height=3em, minimum width=3em,
tmp/.style = coordinate, 
sum/.style= draw, fill=white, circle, node distance=1cm,
input/.style = coordinate,
output/.style= coordinate,
pinstyle/.style = pin edge=to-,thin,black



begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 draw (sum2)|-($(integrator)!.5!(output)!0.5!(sum2)!2cm!90:(sum2)$)node[block]C-|($(integrator)!.5!(output)$);
 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output);

endtikzpicture
enddocument

Old answer:

Nevertheless, here is a solution that includes a series of Parway Modifiers.

documentclassarticle
usepackagetikz,mathtools,amssymb
usetikzlibraryshapes,arrows,positioning,calc

begindocument

tikzset
block/.style = draw, fill=white, rectangle, minimum height=3em, minimum width=3em,
tmp/.style = coordinate, 
sum/.style= draw, fill=white, circle, node distance=1cm,
input/.style = coordinate,
output/.style= coordinate,
pinstyle/.style = pin edge=to-,thin,black



begintikzpicture[auto, node distance=2cm,>=latex',align=center]
 node [sum] (sum2) ;
 node [block, right = 1cm of sum2](ractuator)$frac2s+2$;
 node [block, right = 1cm of ractuator,] (vdynamics) $frac-0.125(s+0.437)(s+1.29)(s+0.193)$;
 node [block, right = 1cm of vdynamics,] (integrator) $frac1s$;
 node [output, right = 1.5cm of integrator] (output) ;
 draw (sum2)|-([yshift=-2cm]$(integrator)!.5!(output)!0.5!(sum2)$)node[block]C-|($(integrator)!.5!(output)$);

 draw [->] (ractuator) -- (vdynamics);
 draw [->] (vdynamics) -- (integrator);
 draw [->] (integrator) -- node[name=heading]$Psi(s)$ (output);

endtikzpicture
enddocument

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