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x-=dx

subtracts dx from x and returns the new value of x.

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Examples  
Basic Examples  
Scope  
Applications  
Properties & Relations  
Possible Issues  
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SubtractFrom

x-=dx

subtracts dx from x and returns the new value of x.

Details

Examples

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Basic Examples  (1)

Wolfram Language code: k = 1;k -= 5
Wolfram Language code: k

Scope  (4)

Subtract from a numerical value:

Wolfram Language code: x = 1.5; x -= 0.75;x

Subtract from a symbolic value:

Wolfram Language code: v = a;v -= b;v

Subtract from all values in a list:

Wolfram Language code: x = {100, 200, 300}
Wolfram Language code: x -= 17;x
Wolfram Language code: x -= {20, 21, 22};x

The first argument to SubtractFrom need not be a symbol:

Wolfram Language code: list = {1, 2, 3}
Wolfram Language code: list[[2]] -= c
Wolfram Language code: list

Applications  (1)

Find the last prime below one million:

Wolfram Language code: i = 10 ^ 6 + 1; While[!PrimeQ[i], i -= 2]; i

Properties & Relations  (3)

SubtractFrom is a short form of this assignment:

Wolfram Language code: k = 1; k = k - 5

PreDecrement is a special case of SubtractFrom:

Wolfram Language code: k = 10; k -= 1
Wolfram Language code: --k

AddTo is closely related:

Wolfram Language code: k = 10; k -= 5
Wolfram Language code: k += -5

Possible Issues  (1)

A variable to be decremented must have an initial value:

Wolfram Language code: x -= 2
Wolfram Research (1988), SubtractFrom, Wolfram Language function, https://reference.wolfram.com/language/ref/SubtractFrom.html.

Text

Wolfram Research (1988), SubtractFrom, Wolfram Language function, https://reference.wolfram.com/language/ref/SubtractFrom.html.

CMS

Wolfram Language. 1988. "SubtractFrom." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/SubtractFrom.html.

APA

Wolfram Language. (1988). SubtractFrom. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/SubtractFrom.html

BibTeX

@misc{reference.wolfram_2026_subtractfrom, author="Wolfram Research", title="{SubtractFrom}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/SubtractFrom.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_subtractfrom, organization={Wolfram Research}, title={SubtractFrom}, year={1988}, url={https://reference.wolfram.com/language/ref/SubtractFrom.html}, note=[Accessed: 13-June-2026]}