# Classical Computations in QUA¶

This section describes standard syntax rules for classical computations in QUA.

## Arithmetic Expressions¶

Multiplication, addition and subtraction of fixed point variables is supported.

Note

division incurs a computational overhead of approximately 400ns per operation.

Operator Symbol Example
multiplication * a * b
division / a / b
subtraction - a - b
with program() as prog:

a = declare(fixed)
b = declare(int)
c = declare(fixed, value=0.3)
d = declare(fixed, value=-0.02)
e = declare(int, value=3)
f = declare(int, value=5)

assign(a, c*d-d+c*0.25)
assign(b, e+f*123*e-e)
assign(c, d/c)

save(a, "a")
save(b, "b")
save(c, "c")


The evaluation of each operator takes only a few clock cycles. For example, the addition (+) and subtraction (-) operations each take 1 clock cycle to evaluate, i.e. 4ns. However, the compiler parallelize operations, resulting in a much reduced effective calculation time which will often be zero.

## Bitwise Operations¶

Left/right bitshifts and bitwise AND, OR, and XOR are supported.

Operator Symbol Usage Example
left bitshift << a << b 6\<\<5 = 192
right bitshift >> a >> b 6>>1 = 3
bitwise AND & a & b 6&5 = 4
bitwise OR | a | b 6|5 = 7
bitwise XOR ^ a ^ b 6^5 = 3

Note

The bitwise NOT operation (~a) is not supported.

## Boolean Operations¶

Boolean operations can be used, but using the operators below ('&', '|', etc) and not with the Pythonic operators ('AND', 'OR', etc)

Warning

Attempting to use Pythonic operators on QUA variables, or attempting to evaluate QUA variables directly (for example, in a Pythonic 'if' statement), would result in an error.

Operator Symbol Example
AND & a & b
OR | a | b
XOR ^ a ^ b
NOT ~ ~a

Compounded boolean expressions are supported.

Note

It is necessary to wrap the atomic boolean expressions in parenthesis as seen in the example below, due to Python operator precedence rules.

Example:

with if_( (~( a > b )) | ( c > d) ):


## Arrays¶

QUA arrays are defined and accessed as follows.

1. declare() a new array:

Syntax:

declare(fixed/int/bool, size=N) - Will create a QUA array of zeros with size N

declare(fixed/int/bool, value=[…]) - Will create a QUA array with the values specified in the list

### Examples:¶

#### Declaration:¶

a1 = declare(int, size=3)
a2 = declare(int, value=[1,2,3])


Note

Specifying both the size and the value parameters is not supported.

Important

Array length is fixed and cannot be changed after declaration.

#### Access cell in array¶

# syntax and examples
assign(a1, 5)
assign(b, a1[i]+6)
assign(a1[i+5], a2[i+4])
save(a1, "v1_2")


Warning

No validation is performed for reading/writing out of bounds.

#### Get array length¶

# syntax and examples
length = declare(int)
assign(length, v1.length())


#### More examples:¶

with program() as arrays_use:

v1 = declare(int, value = [1, 2, 4, 8, 16])
v2 = declare(int, size = 5) # will be initialized with zeros
v3 = declare(fixed, size = 30)  # will be initialized with zeros
i = declare(int)

assign(v3, 16)

with for_(i, 0, i < v2.length(), i + 1):
assign(v2[i], i*2)

with for_(i, 0, i < v1.length(), i + 1):
assign(v2[i], v2[i] + v3[i])

with for_(i, 0, i < v1.length(), i + 1):
save(v1[i], "v1")
save(v2[i], "v2")

with for_(i, 0, i < v3.length(), i + 1):
save(v3[i], "v3")


## Computational library functions¶

QUA allows the user the real time evaluation of several mathematical operators and functions. Besides the standard mathematical operators (+, -, *, /) the user can access various libraries including

• Math - trigonometric functions, array reduction functions etc.
• Random - pseudo-random number generation.
• Cast - allows casting between QUA variable types.
• Utility - Miscellaneous operators, including a hardware optimized conditional expression.

### Math¶

For a full description, please see the Math library reference page.

#### Trigonometric functions¶

• Math.cos(x) : Takes the cosine of a fixed in radians
• Math.sin(x) : Takes the sine of a fixed in radians
• Math.cos2pi(x) : Takes the cosine of a fixed in 2pi radians
• Math.sin2pi(x) : Takes the cosine of a fixed in 2pi radians

cos2pi(x) and sin2pi(x) are equivalent to cos(2*pi*x) and sin(2*pi*x) but saves a few clock cycles as the extra multiplication stage required to calculate 2*pi are removed by simply having 2*pi stored in memory. Moreover, these functions are immune to overflows. So whenever working with radians we suggest using the former. The usage is straightforward, for example:

amplitude = declare(fixed)
time = declare(int)
frequency = declare(int)
assign(amplitude, 1)
assign(frequency, 1e6)
with for_(time, 0, time<100, time+1):
play('pulse_1' * amp(amplitude*Math.cos2pi(frequency*time)), 'element_1')


This program will play pulse_1 for 100 iterations, where for each iteration the amplitude will be modulated by the envelope function cos(2pi * frequency * time). For evaluation of non-real time mathematical expressions one can always use standard python libraries such as numpy.

#### Array reduction¶

QUA provides several function to reduce arrays. These functions run more efficiently (with less latency) when compared to a manual implementing in QUA, as they use hardware optimizations.

• Math.sum(x) : sums an array. The result is of the same type as the input array.
• Math.max(x), Math.min(x) : max,min an array. The result is of the same type as the input array.
• Math.argmin(x)/Math.argmax(x): returns the index of the max/min
• Math.dot(x,y): returns the dot product of two QUA arrays of the same size

#### Others¶

• Math.abs(x) : absolute value of a QUA variable

### Random number generator¶

For a full description, please see the Random library reference page.

This class generates a pseudo-random number using a the LCG algorithm with the following parameters: a = 137939405, c = 12345, m = 2**28.

The class constructor optionally takes a seed number and can generate int or fixed values.

Note

Unless specified explicitly, the seed is selected in python using the RNG module. The seed choice occurs when the program object is created, which means that if we execute a QUA program object several times, the QUA random numbers sequence will be the same for all executions. To have a new seed, one needs to

with program() as prog:
r = Random()
# you can set the seed:
r.set_seed(123213)
a = declare(int)
b = declare(fixed)
assign(a, r.rand_int(100)) # a will be a number between 0 and 99
assign(b, r.rand_fixed()) # b will be a number between 0.0 and 1.0


### Cast¶

For a full description, please see the Casting library reference page.

• Cast.mul_fixed_by_int(x,y): Multiplies a fixed x by an int y, returning a fixed
• Cast.mul_int_by_fixed(x,y): Multiplies an int x by a fixed y, returning an int
• Cast.to_int(x): Casts a variable to int. Supports int, fixed or bool
• Cast.to_fixed(x): Casts a variable to fixed. Supports int, fixed or bool
• Cast.to_bool(x): Casts a variable to bool. Supports int, fixed or bool

### Util¶

For a full description, please see the Utility library reference page.

• Util.cond(a,b,c) : Quick conditional operation.

This is equivalent to a ternary operator available in some languages: i.e. a ? b : c, meaning 'b' if 'a' is true, or 'c' if 'a' is false. There is less computation overhead (less latency) when running this operation relative to the if_ conditional

assign(b, Util.cond(a > b, c, d))